Shares of Its Common Stock for an Aggregate Purchase Price of Not More Than $125 Million

at a Per Share Purchase Price Not Less Than $43.50 Per Share

Nor Greater Than $50.00 Per Share

THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON JANUARY 7, 2016, UNLESS THE OFFER IS
EXTENDED OR TERMINATED (SUCH TIME, AS IT MAY BE EXTENDED, THE EXPIRATION TIME).

Insperity, Inc., a Delaware
corporation (the Company, Insperity, we, our or us), is offering to purchase for cash shares of its common stock, par value $0.01 per share, pursuant to
(i) auction tenders at prices specified by the tendering stockholders of not less than $43.50 nor greater than $50.00 per share (Auction Tenders), or (ii) purchase price tenders (Purchase Price
Tenders), in either case upon the terms and subject to the conditions described in this Offer to Purchase and in the related Letter of Transmittal (the Letter of Transmittal, and together with this Offer to Purchase, as
they may be amended or supplemented from time to time, the Offer). We are offering to purchase shares having an aggregate purchase price of no more than $125 million. Stockholders who wish to tender shares without specifying a
price at which such shares may be purchased by the Company should make a Purchase Price Tender. Under a Purchase Price Tender, we will purchase shares, upon the terms and subject to the conditions of the Offer, at the Purchase Price (as defined
below) determined as provided herein. Stockholders who validly tender shares without specifying whether they are making an Auction Tender or a Purchase Price Tender will be deemed to have made a Purchase Price Tender.

After the Expiration Time, we will, upon the terms and subject to the conditions of the Offer, determine a single price per share (the
Purchase Price), which will be not less than $43.50 and not more than $50.00 per share, that we will pay for shares of our common stock validly tendered in the Offer and not validly withdrawn. Shares tendered pursuant to Purchase
Price Tenders will be deemed to have been tendered at a price of $43.50 per share for purposes of determining the Purchase Price (which is the minimum price per share under the Offer). The Purchase Price will be the lowest price per share of not
less than $43.50 and not more than $50.00 per share, at which shares have been tendered or have been deemed to be tendered in the Offer, that will enable the Company to purchase the maximum number of shares validly tendered in the Offer and not
validly withdrawn having an aggregate purchase price not exceeding $125 million. Only shares validly tendered at prices at or below the Purchase Price, and not validly withdrawn, will be eligible for purchase in the Offer. Shares validly tendered
pursuant to an Auction Tender at a price specified in the Auction Tender that is greater than the Purchase Price will not be purchased. Upon the terms and subject to the conditions of the Offer, if shares having an aggregate purchase price of $125
million or less are validly tendered and not validly withdrawn, we will buy all shares validly tendered and not validly withdrawn. Because of the proration, odd lot priority and conditional tender provisions described in this Offer to
Purchase, all of the shares tendered at or below the Purchase Price may not be purchased if the number of shares validly tendered at or below the Purchase Price and not validly withdrawn have an aggregate purchase price exceeding $125 million.

Assuming that the Offer is fully subscribed, if the Purchase Price is determined to be $43.50 per share, the minimum Purchase Price
under the Offer, the approximate number of shares that would be purchased under the Offer is 2,873,563. Assuming that the Offer is fully subscribed, if the Purchase Price is determined to be $50.00 per share, the maximum Purchase Price under the
Offer, the approximate number of shares that would be purchased under the Offer is 2,500,000.

The Offer is not conditioned upon any
minimum number of shares being tendered. The Offer is, however, subject to a number of other terms and conditions. See Section 7.

Our common stock is listed on the New York Stock Exchange (the NYSE) and trades under the symbol
NSP. On December 7, 2015, the reported closing price of our common stock on the NYSE was $44.03 per share. You are urged to obtain current market quotations for our common stock before deciding whether, and at what price or
prices, to tender your shares pursuant to the Offer. See Section 8.

Neither the Securities and Exchange Commission nor any state securities commission has
approved or disapproved of this transaction or passed upon the merits or fairness of such transaction or passed upon the adequacy or accuracy of the information contained in this Offer to Purchase. Any representation to the contrary is a criminal
offense.

If you have questions or need assistance, you should contact the Information Agent or the Dealer Manager at their respective
telephone numbers and addresses set forth on the back cover page of this Offer to Purchase. If you require additional copies of this Offer to Purchase, the Letter of Transmittal or other documents relating to the Offer, you should contact the
Information Agent.

THE COMPANYS BOARD OF DIRECTORS HAS APPROVED THE OFFER. HOWEVER, NONE OF THE COMPANYS BOARD OF DIRECTORS, THE DEALER MANAGER, THE
DEPOSITARY OR THE INFORMATION AGENT MAKES ANY RECOMMENDATION TO YOU AS TO WHETHER TO TENDER OR REFRAIN FROM TENDERING YOUR SHARES OR AS TO THE PRICE OR PRICES AT WHICH YOU MAY CHOOSE TO TENDER YOUR SHARES. WE HAVE NOT AUTHORIZED ANY PERSON TO MAKE
ANY SUCH RECOMMENDATION. YOU MUST MAKE YOUR OWN DECISIONS AS TO WHETHER TO TENDER YOUR SHARES AND, IF SO, HOW MANY SHARES TO TENDER AND THE PRICE OR PRICES AT WHICH YOU WILL TENDER THEM. IN DOING SO, YOU SHOULD READ CAREFULLY THE INFORMATION IN, OR
INCORPORATED BY REFERENCE IN, THIS OFFER TO PURCHASE AND IN THE LETTER OF TRANSMITTAL, INCLUDING THE PURPOSES AND EFFECTS OF THE OFFER. SEE SECTION 2. YOU ARE URGED TO DISCUSS YOUR DECISIONS WITH YOUR OWN TAX ADVISER, FINANCIAL ADVISER AND/OR
BROKER.

Our directors and executive officers do not intend to tender their shares in the Offer. We are not aware of any of our affiliates
that intend to tender any shares in the Offer. In addition, Starboard Value LP (together with its affiliates and certain related funds, Starboard), which owned approximately 13.74% of our shares as of December 1, 2015, has
advised us that it does not intend to participate in the Offer. See Section 11.

To validly tender all or any portion of your shares,
you must do one of the following prior to the Expiration Time:



if your shares are registered in the name of a broker, dealer, commercial bank, trust company or other nominee, contact the nominee and have the nominee tender your shares for you;



if you hold certificates in your own name, complete and sign a Letter of Transmittal according to its instructions and deliver it, together with any required signature guarantees, the certificates for your shares and
any other documents required by the Letter of Transmittal, to Computershare Trust Company, N.A., the Depositary for the Offer, at one of the addresses shown on the Letter of Transmittal;



if you are an institution participating in The Depository Trust Company (DTC) and you hold your shares through DTC, tender your shares according to the procedure for book-entry transfer described in
Section 3; or



if you are a holder of vested options to purchase shares of our common stock, subject to Company policies and practices, you may exercise your vested options to purchase shares and tender such shares in the Offer;
however, we suggest that you exercise your vested options at least five business days prior to the date on which the Expiration Time is initially scheduled to occur (which, unless the Offer is extended, will require you to exercise such options no
later than 5:00 p.m., New York City time, on December 30, 2015) in order to provide you with sufficient time to validly tender the shares in the Offer. Exercises of options cannot be revoked even if some or all of the shares received upon the
exercise thereof and tendered in the Offer are not purchased pursuant to the Offer for any reason.

If you want to tender
your shares but your certificates for the shares are not immediately available, or cannot be delivered to the Depositary within the required time, or you cannot comply with the procedure for book-entry transfer on a timely basis, or your other
required documents cannot be delivered to the Depositary prior to the Expiration Time, you may still tender your shares if you comply with the guaranteed delivery procedure described in Section 3 of this Offer to Purchase.

Beneficial owners should be aware that their broker, dealer, commercial bank, trust company or other nominee may establish its own earlier
deadline for participation in the Offer. Accordingly, beneficial owners wishing to participate in the Offer should contact their broker, dealer, commercial bank, trust company or other nominee as soon as possible in order to determine the times by
which such owner must take action in order to participate in the Offer.

Under a Purchase Price Tender, we will purchase shares, upon the terms and subject to the
conditions of the Offer, at the Purchase Price. If you wish to maximize the chance that we will purchase your shares, you should validly tender your shares pursuant to a Purchase Price Tender. Shares tendered pursuant to Purchase Price Tenders will
be deemed to have been tendered at a price of $43.50 per share (which is the minimum price per share under the Offer) for purposes of determining the Purchase Price. Accordingly, Purchase Price Tenders could result in the Purchase Price being lower
and could result in your shares being purchased at the minimum price in the Offer. The lower end of the price range for the Offer is below the closing market price on the NYSE for the shares of $44.03 on December 7, 2015, the last full trading day
before we commenced the Offer.

We are not making the Offer to, and will not accept any tendered shares from, stockholders in any
jurisdiction where it would be illegal to do so. However, we may, at our discretion, take any actions necessary for us to make the Offer to stockholders in any such jurisdiction. In any jurisdiction where the securities or blue sky laws thereof
require the Offer to be made by a licensed broker or dealer, the Offer is being made on our behalf by the Dealer Manager or one or more registered brokers or dealers, which are licensed under the laws of such jurisdiction.

Questions and requests for assistance may be directed to Innisfree M&A Incorporated, the information agent for the Offer (the
Information Agent), and Credit Suisse Securities (USA) LLC, the dealer manager for the Offer (the Dealer Manager), at their respective telephone numbers and addresses set forth on the back cover page of this
Offer to Purchase. You may request additional copies of this Offer to Purchase, the Letter of Transmittal and other Offer documents from the Information Agent at the telephone numbers and address on the back cover page of this Offer to Purchase.
Stockholders may also contact their broker, dealer, commercial bank, trust company or other nominee for assistance concerning the Offer.

We have not authorized any person to make any recommendation on our behalf as to whether you should tender or refrain from tendering your
shares in the Offer or as to the price or prices at which you may choose to tender your shares in the Offer. You should rely only on the information contained in this Offer to Purchase and in the Letter of Transmittal or in documents to which we
have referred you. Our delivery of this Offer to Purchase shall not under any circumstances create any implication that the information contained in this Offer to Purchase is correct as of any time other than the date of this Offer to Purchase or
that there have been no changes in the information included or incorporated by reference herein or in the affairs of Insperity or any of its subsidiaries or affiliates since the date hereof. We have not authorized anyone to provide you with
information or to make any representation in connection with the Offer other than the information and representations contained in this Offer to Purchase or in the Letter of Transmittal. If anyone makes any recommendation or gives any information or
representation, you must not rely upon that recommendation, information or representation as having been authorized by us, the Dealer Manager, the Depositary or the Information Agent.

We are providing this summary term sheet for your convenience. This summary term sheet highlights certain material information in this
Offer to Purchase, but you should realize that it does not describe all of the details of the Offer to the same extent described elsewhere in this Offer to Purchase. To understand the Offer fully and for a more complete description of the terms of
the Offer, you should read carefully this entire Offer to Purchase, the Letter of Transmittal and the other documents relating to the Offer. We have included references to the sections of this Offer to Purchase where you will find a more complete
description of the topics in this summary.

Who is offering to purchase the shares of common stock?

The issuer of the shares, Insperity, Inc., is offering to purchase the shares.

What will be the Purchase Price for the shares and what will be the form of payment?

We are conducting an offer by means of a procedure commonly called a modified Dutch auction. Upon the terms and subject to
the conditions of the Offer, we are offering to purchase for cash shares of our common stock, par value $0.01 per share, pursuant to (i) Auction Tenders at prices specified by the tendering stockholders of not less than $43.50 nor greater than
$50.00 per share or (ii) Purchase Price Tenders. We are offering to purchase shares having an aggregate purchase price of no more than $125 million. Promptly after 5:00 p.m., New York City time, on January 7, 2016, unless the Offer is
extended or terminated (such time, as it may be extended, the Expiration Time), we will, upon the terms and subject to the conditions of the Offer, determine a single price per share, the Purchase Price, which will be not less
than $43.50 and not more than $50.00 per share, that we will pay for shares validly tendered in the Offer and not validly withdrawn, taking into account the number of shares tendered pursuant to Auction Tenders and pursuant to Purchase Price Tenders
and the prices specified by stockholders tendering shares pursuant to Auction Tenders. Shares tendered pursuant to Purchase Price Tenders will be deemed to have been tendered at a price of $43.50 per share (which is the minimum price per share under
the Offer) for purposes of determining the Purchase Price.

The Purchase Price will be the lowest price per share of not less than
$43.50 and not more than $50.00 per share at which shares have been tendered or have been deemed to be tendered in the Offer that will enable us to purchase the maximum number of shares validly tendered and not validly withdrawn in the Offer having
an aggregate purchase price not exceeding $125 million. We will publicly announce the Purchase Price promptly after we have determined it and, upon the terms and subject to the conditions of the Offer (including the proration provisions), we
will pay the Purchase Price in cash, subject to applicable withholding taxes and without interest, to all stockholders whose shares are accepted for payment pursuant to the Offer. See Section 1.

If you wish to maximize the chance that your shares will be purchased by us, you should validly tender your shares pursuant to a Purchase
Price Tender. Shares tendered pursuant to Purchase Price Tenders will be deemed to have been tendered at a price of $43.50 per share (which is the minimum price per share under the Offer) for purposes of determining the Purchase Price. Accordingly,
Purchase Price Tenders could result in the Purchase Price being lower and could result in your shares being purchased at the minimum price in the Offer of $43.50 per share.

How many shares of its common stock is Insperity offering to purchase?

Upon the terms and subject to the conditions of the Offer, we are offering to purchase, at the Purchase Price, shares of common stock validly
tendered in the Offer and not validly withdrawn up to a maximum aggregate purchase price of $125 million. Because the Purchase Price will only be determined after the Expiration Time, the number of shares that will be purchased will not be
known until after that time. Assuming that the Offer is fully subscribed, if the Purchase Price is determined to be $43.50 per share, the minimum Purchase Price under

the Offer, the approximate number of shares that would be purchased under the Offer is 2,873,563. Assuming that the Offer is fully subscribed, if the Purchase Price is determined to be $50.00 per
share, the maximum Purchase Price under the Offer, the approximate number of shares that would be purchased under the Offer is 2,500,000. Assuming that the Offer is fully subscribed, the maximum of 2,873,563 shares that the Company is offering to
purchase under the Offer would represent approximately 11.8% of the total number of shares issued and outstanding as of December 1, 2015. Assuming the Offer is fully subscribed, the minimum of 2,500,000 shares that the Company is offering to
purchase under the Offer would represent approximately 10.3% of the total number of shares issued and outstanding as of December 1, 2015.

The Offer is not conditioned upon any minimum number of shares being tendered. The Offer is, however, subject to a number of other terms and
conditions. See Section 7.

How will Insperity pay for the shares?

We intend to fund any purchase of shares pursuant to the Offer, including the related fees and expenses, with borrowings under our revolving
credit facility and from cash on hand. The Offer is not subject to a financing contingency. See Section 9.

How long do I have to tender my
shares?

You may tender your shares until the Offer expires at the Expiration Time. The Offer will expire at 5:00 p.m., New York
City time, on January 7, 2016, unless we extend or terminate the Offer. See Sections 4, 7 and 15.

If a broker, dealer, commercial
bank, trust company or other nominee holds your shares, it is likely that they will have an earlier deadline for you to act to instruct them to accept the Offer on your behalf. We urge you to immediately contact your broker, dealer, commercial bank,
trust company or other nominee to find out their deadline. See Sections 1 and 3.

Can the Offer be extended, amended or terminated and, if so, under
what circumstances?

We may extend the Expiration Time for the Offer in our sole discretion at any time, subject to applicable laws. We
may, however, decide not to extend the Expiration Time for the Offer. If we were to extend the Expiration Time for the Offer, we cannot indicate, at this time, the length of any extension that we may provide. If we extend the Expiration Time for the
Offer, we will delay the acceptance of any shares that have been tendered, and any shares that have been previously tendered may be withdrawn up until the Expiration Time, as so extended. We may also amend or terminate the Offer, subject to
applicable law. See Sections 4, 7 and 15.

How will I be notified if the Offer is extended, amended or terminated?

If the Expiration Time for the Offer is extended, we will issue a press release announcing the extension and the new Expiration Time no later
than 9:00 a.m., New York City time, on the first business day after the last previously scheduled Expiration Time. We will announce any amendment to or termination of the Offer by issuing a press release announcing the amendment or termination. See
Section 15.

What is the purpose of the Offer?

Our Board of Directors, with the assistance of management, has decided to conduct the Offer after reviewing a variety of alternatives for using
our available financial resources. Our Board considered our existing and anticipated capitalization and financial position, including our outstanding common stock, liquidity, cash position, working capital, our lack of long-term debt, and our
operations, strategy and expectations for the future.

The Board believes that the Offer represents a prudent use of our financial resources in light of
our business profile, assets, current indebtedness and debt capacity. At September 30, 2015, we had working capital of $76.4 million, no long-term debt and $124.4 million of available borrowing capacity under our existing revolving credit
facility. The primary purpose of the Offer is to return cash to our stockholders by providing them with the opportunity to tender all or a portion of their shares and, thereby, receive a return of some or all of their investment if they so elect. In
addition, if we complete the Offer, stockholders who do not participate in the Offer will automatically increase their relative percentage ownership interest in us and our future operations.

Assuming the Offer is fully subscribed, we believe that our anticipated cash flow from operations, our access to credit and capital markets
and our financial condition will be adequate for our needs. However, actual results may differ significantly from our expectations. See Forward-Looking Statements. In considering the Offer, our management and our Board of Directors took
into account the expected financial impact of the Offer on our liquidity.

After the completion or termination of the Offer, we may
purchase additional shares in the open market subject to market conditions. We may also purchase shares in private transactions, tender offers or otherwise. Any of these purchases may be on the same terms as, or on terms more or less favorable to
stockholders than, the terms of the Offer. However, Rule 13e-4 under the Securities Exchange Act of 1934, as amended (the Exchange Act), generally prohibits us and our affiliates from purchasing any shares, other than through the
Offer, until at least 10 business days after the expiration or termination of the Offer. Any possible future purchases by us will depend on many factors, including the market price of the shares, the results of the Offer, our business and financial
position and general economic and market conditions. See Section 2.

What are the conditions to the Offer?

Our obligation to accept and purchase and pay for shares tendered in the Offer depends upon a number of conditions that must be satisfied or
waived prior to the Expiration Time, including that:



no action, suit, proceeding or application by any government or governmental, regulatory or administrative agency, authority or tribunal or by any other person, domestic or foreign, before any court, authority, agency,
other tribunal or arbitrator or arbitration panel shall have been instituted or shall be pending, nor shall we have received notice of any such action, that directly or indirectly (1) challenges or seeks to challenge, restrain, prohibit, delay
or otherwise affect the making of the Offer, the acquisition by us of some or all of the shares pursuant to the Offer or otherwise relates in any manner to the Offer or seeks to obtain material damages in respect of the Offer or (2) seeks to
make the purchase of, or payment for, some or all of the shares pursuant to the Offer illegal or may result in a delay in our ability to accept for payment or pay for some or all of the shares;



our acceptance for payment, purchase or payment for any shares tendered in the Offer shall not violate or conflict with, or otherwise be contrary to, any applicable law, statute, rule, regulation, decree or order;



no action shall have been taken nor any statute, rule, regulation, judgment, decree, injunction or order (preliminary, permanent or otherwise) shall have been proposed, sought, enacted, entered, promulgated, enforced or
deemed to be applicable to the Offer or us or any of our subsidiaries by any court, government or governmental agency or other regulatory or administrative authority or body, domestic or foreign, which (1) indicates that any approval or other
action of any such court, agency or authority may be required in connection with the Offer or the purchase of shares thereunder or (2) is reasonably likely to make the purchase of, or payment for, some or all of the shares pursuant to the Offer
illegal or to prohibit, restrict or delay consummation of the Offer;



no general suspension of trading in securities on any United States national securities exchange or in the over-the-counter market, declaration of a
banking moratorium or any suspension of payments in respect of banks in the United States, whether or not mandatory, or any limitation, whether or not

mandatory, by any governmental, regulatory or administrative agency or authority on, or any event that is likely, in our reasonable judgment, to materially adversely affect, the extension of
credit by banks or other lending institutions in the United States shall have occurred;



no commencement or escalation, on or after December 7, 2015, of war, armed hostilities or other international or national calamity, including, but not limited to, an act of terrorism involving the United States;



no decrease of more than 10% in the market price for our common stock or in the Dow Jones Industrial Average, New York Stock Exchange Index, the New York Stock Exchange Composite Index or the Standard and Poors
500 Composite Index measured from the close of trading on December 7, 2015 shall have occurred;



no change, condition, event or development, or any condition, event or development involving a prospective change, occurs, is discovered, or is threatened relating to (i) general political, market, economic,
financial or industry conditions in the United States or (ii) our business, general affairs, management, financial position, stockholders equity, income, results of operations, properties, assets, liabilities, condition (financial or
otherwise), income, operations, licenses, permits, or prospects or in ownership of our shares, which in our reasonable judgment is or may be materially adverse to us or otherwise makes it inadvisable for us to proceed with the Offer;



in the case of any of the matters described in the preceding four bullets existing at the time of the announcement of the Offer, as applicable, no material acceleration or worsening thereof;



no tender or exchange offer for any or all of our outstanding common stock (other than the Offer), or any merger, amalgamation, acquisition, business combination or other similar transaction with or involving us or any
of our subsidiaries, shall have been proposed, announced or made by any person or entity or shall have been publicly disclosed, nor shall we have entered into a definitive agreement or an agreement in principle with any person with respect to a
merger, amalgamation, acquisition, business combination or other similar transaction;



we shall not have learned that any entity, group (as that term is used in Section 13(d)(3) of the Exchange Act) or person (1) has acquired or proposes to acquire beneficial ownership of more than
5% of our outstanding common stock, whether through the acquisition of stock, the formation of a group, the grant of any option or right (options for and other rights to acquire shares of common stock that are acquired or proposed to be acquired
being deemed to be immediately exercisable or convertible for purposes of this clause), or otherwise (other than anyone who publicly disclosed such ownership in a filing with the Securities and Exchange Commission (the
SEC) on or before December 7, 2015), (2) who has filed a Schedule 13D or Schedule 13G with the SEC on or before December 7, 2015 has acquired or proposes to acquire, whether through the acquisition of
shares, the formation of a group, the grant of any option or right (options for and other rights to acquire shares of our common stock that are acquired or proposed to be acquired being deemed to be immediately exercisable or convertible for
purposes of this clause), or otherwise (other than by virtue of consummation of the Offer), beneficial ownership of an additional 1% or more of our outstanding common stock or (3) shall have filed a Notification and Report Form under the
Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, reflecting an intent to acquire us or any of our subsidiaries or any of our or their respective assets or securities;



no approval, permit, authorization, favorable review or consent or waiver of or filing with any domestic or foreign governmental entity or other authority or any third party consent or notice, required to be obtained or
made in connection with the Offer shall not have been obtained or made on terms and conditions satisfactory to us in our reasonable judgment; or



we shall not have determined that the consummation of the Offer and the purchase of the shares pursuant to the Offer is likely, in our reasonable judgment, to cause our common stock to be delisted from the NYSE or
eligible for deregistration under the Exchange Act.

How will the Offer affect the number of our shares outstanding and the number of record holders?

As of December 1, 2015, we had 24,277,515 issued and outstanding shares. At the minimum Purchase Price of $43.50 per share, we would
purchase 2,873,563 shares if the Offer is fully subscribed, which would represent approximately 11.8% of our outstanding shares as of December 1, 2015. At the maximum Purchase Price of $50.00 per share, we would purchase 2,500,000 shares if the
Offer is fully subscribed, which would represent approximately 10.3% of our outstanding shares as of December 1, 2015. If the Offer is fully subscribed at the minimum Purchase Price, we would have approximately 21,403,952 shares outstanding
immediately following the purchase of shares tendered in the Offer. If the Offer is fully subscribed at the maximum Purchase Price, we would have approximately 21,777,515 shares outstanding immediately following the purchase of shares tendered in
the Offer. The actual number of shares outstanding immediately following completion of the Offer will depend on the number of shares tendered and purchased in the Offer as well as the Purchase Price for such shares. See Section 2.

If any of our stockholders:



who hold shares in their own name as holders of record; or



who are registered holders as participants in the DTCs system whose names appear on a security position listing,

tender their shares in full and that tender is accepted in full, then the number of our record holders would be reduced. See Section 2.

Stockholders who do not have their shares purchased in the Offer will realize a proportionate increase in their relative ownership interest in
the Company following the purchase of shares pursuant to the Offer. See Section 2.

Will the Company continue as a public company following the
Offer?

We believe that our purchase of shares pursuant to the Offer will not result in delisting of the remaining shares on the NYSE
or the shares becoming eligible for termination of registration under the Exchange Act. The Offer is conditioned upon, among other things, our having determined that the consummation of the Offer will not cause the shares to be delisted from the
NYSE or to be eligible for deregistration under the Exchange Act. See Sections 2, 7 and 12.

How do I validly tender my shares?

To validly tender all or any portion of your shares, you must do one of the following prior to the Expiration Time:



if your shares are registered in the name of a broker, dealer, commercial bank, trust company or other nominee, contact the nominee and have the nominee tender your shares for you;



if you hold certificates in your own name, complete and sign a Letter of Transmittal according to its instructions and deliver it, together with any required signature guarantees, the certificates for your shares and
any other documents required by the Letter of Transmittal, to Computershare Trust Company, N.A., the Depositary for the Offer, at one of the addresses shown on the Letter of Transmittal;



if you are an institution participating in DTC and you hold your shares through DTC, tender your shares according to the procedure for book-entry transfer described in Section 3 of this Offer to Purchase; or

if you are a holder of vested options to purchase shares of our common stock, subject to Company policies and practices, you may exercise your vested options to purchase shares and tender such shares in the Offer;
however, we suggest that you exercise your vested options at least five business days prior to the Expiration Time (which, unless the Offer is extended, will require you to exercise such options no later than 5:00 p.m., New York City time, on
December 30, 2015) in order to provide you with sufficient time to validly tender the shares in the Offer. Exercises of options cannot be revoked even if some or all of the shares received upon the exercise thereof and tendered in the Offer are
not purchased pursuant to the Offer for any reason.

In accordance with Instructions 4 and 5 to the Letter of Transmittal,
each stockholder who is not tendering through DTC and who desires to tender shares in the Offer must either check (1) one, and only one, of the boxes in the section of the Letter of Transmittal captioned Auction Price Tender: Price (in
Dollars) per Share at Which Shares are Being Tendered, indicating the price (in increments of $0.25) at which shares are being tendered, or (2) the box in the section of the Letter of Transmittal captioned Purchase Price
Tender, in which case you will be deemed to have tendered your shares at the minimum price of $43.50 per share (you should understand that this election may cause the Purchase Price to be lower and could result in the tendered shares being
purchased at the minimum price of $43.50 per share).

If tendering stockholders wish to maximize the chance that we will purchase their
shares, they should check the box in the section of the Letter of Transmittal captioned Purchase Price Tender. Shares tendered pursuant to Purchase Price Tenders will be deemed to have been tendered at a price of $43.50 per share (which
is the minimum price per share under the Offer) for purposes of determining the Purchase Price. Accordingly, Purchase Price Tenders could result in the Purchase Price being lower and could result in your shares being purchased at the minimum
price in the Offer. See Section 8 for recent market prices for shares of our common stock.

If you want to tender your shares but
(a) your certificates for the shares are not immediately available, or cannot be delivered to the Depositary within the required time, (b) you cannot comply with the procedure for book-entry transfer on a timely basis, or (c) your
other required documents cannot be delivered to the Depositary prior to the Expiration Time, you may still tender your shares if you comply prior to the Expiration Time with the guaranteed delivery procedure described in Section 3.

Beneficial owners should be aware that their broker, dealer, commercial bank, trust company or other nominee may establish its own earlier
deadline for participation in the Offer. Accordingly, beneficial owners wishing to participate in the Offer should contact their broker, dealer, commercial bank, trust company or other nominee as soon as possible in order to determine the times by
which such owner must take action in order to participate in the Offer.

You may contact the Information Agent, the Dealer Manager or your
broker, dealer, commercial bank, trust company or other nominee for assistance. The contact information for the Information Agent and the Dealer Manager is on the back cover page of this Offer to Purchase. See Section 3 and the instructions to
the Letter of Transmittal.

May I tender only a portion of the shares that I hold?

Yes. You do not have to tender all of the shares that you own to participate in the Offer.

How do holders of vested stock options for shares participate in the Offer?

Options to purchase shares of our common stock cannot be tendered in the Offer. If you hold vested but unexercised options, you may exercise
such options in accordance with the terms of our equity-based compensation plans and the Companys policies and practices, and tender the shares received upon such exercise

in accordance with the Offer. Exercises of options cannot be revoked even if some or all of the shares received upon the exercise thereof and tendered in the Offer are not purchased pursuant to
the Offer for any reason. You should evaluate this Offer to Purchase carefully to determine if participation would be advantageous to you based on your stock option exercise prices and the expiration date of your options, the range of tender prices
and the provisions for pro rata purchases by Insperity described in Section 1. We strongly encourage optionholders to discuss the Offer with their own tax advisers, financial advisers and/or brokers.

Please be advised that it is the optionholders responsibility to tender shares in the Offer to the extent such holder wants to
participate and it may be difficult to secure delivery of shares issued pursuant to the exercise of vested stock options in a time period sufficient to allow tender of those shares prior to the Expiration Time. Accordingly, we suggest that you
exercise your vested options and satisfy the exercise price for such shares in accordance with the terms of the related stock option plan and option agreement and Company policies and practices at least five business days prior to the date on which
the Expiration Time is initially scheduled to occur (which, unless the Offer is extended, means you should exercise your vested stock options and satisfy the related exercise price no later than 5:00 p.m., New York City time, on December 30,
2015). Exercises of options cannot be revoked even if some or all of the shares received upon the exercise thereof and tendered in the Offer are not purchased pursuant to the Offer for any reason. See Section 3.

May holders of restricted stock awards participate in the Offer?

Holders of restricted stock awards may not tender such restricted stock in the Offer unless and until such shares have vested and any other
restrictions on such shares have lapsed. See Section 3.

In what order will Insperity purchase the tendered shares?

If the terms and conditions of the Offer have been satisfied or waived and shares having an aggregate purchase price of $125 million or less
are validly tendered and not validly withdrawn, we will buy all shares validly tendered and not validly withdrawn.

If the terms and
conditions of the Offer have been satisfied or waived and shares having an aggregate purchase price in excess of $125 million, measured at the maximum price at which such shares were validly tendered, have been validly tendered and not validly
withdrawn, we will purchase shares in the following order of priority:



First, all shares owned in odd lots (less than 100 shares) that have been validly tendered at or below the Purchase Price (and not validly withdrawn) (tenders of less than all of the shares owned,
beneficially or of record, by such odd lot shareholders will not qualify for this preference);



Second, all other tendered shares (other than conditionally tendered shares for which the condition was not satisfied) validly tendered at or below the Purchase Price (and not validly withdrawn), on a pro rata
basis if necessary, with appropriate adjustments to avoid the purchase of fractional shares (except for stockholders who tendered shares conditionally for which the condition was not satisfied), until we have purchased shares resulting in an
aggregate purchase price of $125 million; and



Third, if necessary to permit us to purchase shares having an aggregate purchase price of $125 million, such shares conditionally validly tendered at or below the Purchase Price (and not validly withdrawn) for
which the condition was not initially satisfied, to the extent feasible, by random lot (to be eligible for purchase by random lot, stockholders whose shares are conditionally tendered must have tendered all of their shares). See Sections 1 and 6.

If I own fewer than 100 shares and I tender all of my shares, will I be subject to proration?

If you own, beneficially or of record, fewer than 100 shares in the aggregate, you validly tender all of these shares at or below the Purchase
Price (and do not validly withdraw such shares) and you complete the section

entitled Odd Lots in the Letter of Transmittal and, if applicable, in the Notice of Guaranteed Delivery, and all conditions to the Offer are satisfied or waived, we will purchase all
of your shares without subjecting them to proration. See Section 1.

Once I have tendered shares in the Offer, can I withdraw my tender?

Yes. You may withdraw your tendered shares at any time prior to the Expiration Time. In addition, unless we have already accepted your tendered
shares for payment, you may withdraw your tendered shares at any time after 11:59 p.m., New York City time, on February 9, 2016. See Section 4.

How do I validly withdraw shares previously tendered?

To validly withdraw tendered shares, you must deliver, on a timely basis, a written or facsimile notice of your withdrawal to the Depositary,
at its address set forth on the back cover page of this Offer to Purchase, while you still have the right to withdraw the shares. Your notice of withdrawal must specify your name, the number of shares to be withdrawn, the price at which such shares
were tendered, if an Auction Tender is being withdrawn, and the name of the registered holder of such shares. Some additional requirements apply if the certificates for shares to be withdrawn have been delivered to the Depositary or if your shares
have been tendered under the procedure for book-entry transfer set forth in Section 3. If you have tendered your shares by giving instructions to a broker, dealer, commercial bank, trust company or other nominee, you must instruct that person
to arrange for the withdrawal of your shares. You should note that your broker, dealer, commercial bank, trust company or other nominee through which you have tendered shares, will likely have an earlier deadline than the Expiration Time for you to
act to instruct them to withdraw a tender pursuant the Offer. See Section 4.

Has Insperity or its Board of Directors adopted a position on the
Offer?

While our Board of Directors has approved the Offer, none of our Board of Directors, the Dealer Manager, the Information Agent
or the Depositary has made, or is making, any recommendation to you as to whether you should tender or refrain from tendering your shares or as to the price or prices at which you may choose to tender your shares. We have not authorized any person
to make any such recommendation. You must make your own decisions as to whether to tender your shares and, if so, how many shares to tender and the price or prices at which you will tender them. In doing so, you should read carefully the information
in, or incorporated by reference in, this Offer to Purchase and in the Letter of Transmittal, including the purposes and effects of the Offer. You are urged to discuss your decisions with your own tax adviser, financial adviser and/or broker. See
Section 2.

Do Insperitys directors or executive officers or affiliates intend to tender their shares in the Offer?

Our directors and executive officers do not intend to tender their shares in the Offer. We are not aware of any of our affiliates that intend
to tender any shares in the Offer. In addition, Starboard, which owned approximately 13.74% of our shares as of December 1, 2015, has advised us that it does not intend to participate in the Offer. See Section 11.

What will happen if I do not tender my shares?

Stockholders who do not participate in the Offer will retain their shares and, if the Company completes the Offer, their relative ownership
interest in the Company will automatically increase. See Section 2.

When and how will Insperity pay for my tendered shares that are accepted for
purchase pursuant to the Offer?

We will pay the Purchase Price in cash, less any applicable withholding taxes and without interest,
for the shares we purchase promptly after the expiration of the Offer and the acceptance of the shares for payment. We

expect that it may take up to four business days after the Expiration Time to calculate the final proration factor, if any, and begin paying for tendered shares. We will pay for the shares
accepted for purchase by depositing the aggregate purchase price with the Depositary promptly after the expiration of the Offer. The Depositary will act as your agent and will transmit to you the payment for all of your shares accepted for payment
pursuant to the Offer. See Section 5.

What is the recent market price for the Companys common stock?

On December 7, 2015, the reported closing price of our common stock on the NYSE was $44.03 per share. The lower end of the price
range for the Offer of $43.50 per share is below the closing market price on the NYSE for the shares of $44.03 on December 7, 2015, the last full trading day before we commenced the Offer. You are urged to obtain current market quotations for our
common stock before deciding whether, and at what price or prices, to tender your shares pursuant to the Offer. See Section 8.

Will I have to
pay brokerage fees and commissions if I tender my shares?

If you are a holder of record of your shares and you tender your shares
directly to the Depositary, you will not incur any brokerage fees or commissions. If you hold your shares through a broker, dealer, commercial bank, trust company or other nominee and that person tenders shares on your behalf, that person may charge
you a fee or commission for doing so. We urge you to consult your broker, dealer, commercial bank, trust company or other nominee to determine whether any such charges will apply. See Section 3.

What is the accounting treatment of the Offer?

The accounting for the purchase of shares pursuant to the Offer will result in a reduction of our stockholders equity in an amount equal
to the aggregate purchase price of the shares we purchase and related transaction costs, and a related reduction in cash and cash equivalents and increase in long-term debt. See Sections 2 and 9.

I am a U.S. stockholder. What are the U.S. federal income tax consequences if I tender my shares?

Generally, if you are a U.S. Holder (as defined in Section 14) you will be subject to U.S. federal income taxation when you receive cash
from us in exchange for the shares you tender. Your receipt of cash for your tendered shares generally will be treated for U.S. federal income tax purposes as either (1) consideration received in a sale or exchange or (2) a distribution
with respect to such shares. See Sections 3 and 14.

Each stockholder is advised to consult its own tax adviser to determine the U.S.
federal, state, local, foreign and other tax consequences to it of the Offer.

I am a foreign stockholder. What are the U.S. federal income tax
consequences if I tender my shares?

If you are a Non-U.S. Holder (as defined in Section 14), your receipt of cash for your
tendered shares generally will be treated as either (1) consideration received in a sale or exchange or (2) a distribution with respect to such shares. If the receipt of cash by you is treated as consideration received in a sale or
exchange, and you are not engaged in a trade or business in the United States, you generally will not be subject to U.S. federal income taxation on the receipt of such cash subject to certain exceptions. However, if the receipt of cash is treated as
a distribution with respect to your tendered shares, you may be subject to tax on the portion of such distribution treated as a dividend for U.S. federal income tax purposes at a rate of 30% (or a lower rate pursuant to an applicable
income tax treaty). The treatment of the receipt of cash depends upon facts which may be unique as to each stockholder. Therefore, as to each Non-U.S. Holder, U.S. federal income tax will be withheld at a 30% rate unless such Non-U.S. Holder
provides documentation pursuant to which the Depositary, or other withholding agent, may determine that an exemption from, or reduction of, such withholding applies. If tax has been withheld but the receipt of cash for your tendered shares is
treated as consideration received in a sale or exchange, then, in an appropriate case, you may apply for a refund of such withheld amount. See Sections 3 and 14.

Each stockholder is advised to consult its own tax adviser to determine the U.S. federal,
state, local, foreign and other tax consequences to it of the Offer.

Will I have to pay a stock transfer tax if I tender my shares?

If you instruct the Depositary in the Letter of Transmittal to make the payment for the tendered shares to the registered holder, you will not
incur any stock transfer tax. See Section 5.

Whom do I contact if I have questions about the Offer?

For additional information or assistance, you may contact Innisfree M&A Incorporated, the Information Agent for the Offer, or Credit Suisse
Securities (USA) LLC, the Dealer Manager for the Offer, in each case at the telephone numbers and addresses set forth on the back cover page of this Offer to Purchase. You may request additional copies of this Offer to Purchase, the Letter of
Transmittal and other Offer documents from the Information Agent at its telephone numbers and address on the back cover page of this Offer to Purchase. The Information Agent will promptly furnish to stockholders additional copies of these materials
at the Companys expense. Stockholders may also contact their broker, dealer, commercial bank, trust company or other nominee for assistance concerning the Offer.

This Offer to Purchase and the documents incorporated by reference herein may contain forward-looking statements. You can identify
such forward-looking statements by the words expects, intends, plans, projects, believes, estimates, likely, possibly, probably,
goal, opportunity, objective, target, assume, outlook, guidance, predicts, appears, indicator and similar expressions.
Forward-looking statements involve a number of risks and uncertainties. In the normal course of business, we, in an effort to help keep our stockholders and the public informed about our operations, may from time to time issue such forward-looking
statements, either orally or in writing. Generally, these statements relate to business plans or strategies, projected or anticipated benefits or other consequences of such plans or strategies, or projections involving anticipated revenues,
earnings, unit growth, profit per worksite employee, pricing, operating expenses or other aspects of operating results. We base the forward-looking statements on our expectations, estimates and projections at the time such statements are made. These
statements are not guarantees of future performance and involve risks and uncertainties that we cannot predict. In addition, we have based many of these forward-looking statements on assumptions about future events that may prove to be inaccurate.
Therefore, the actual results of the future events described in such forward-looking statements could differ materially from those stated in such forward-looking statements. Among the factors that could cause actual results to differ materially are:
(i) adverse economic conditions; (ii) regulatory and tax developments and possible adverse application of various federal, state and local regulations; (iii) the ability to secure competitive replacement contracts for health insurance
and workers compensation insurance at expiration of current contracts; (iv) cancellation of client contracts on short notice, or the inability to renew client contracts or attract new clients; (v) vulnerability to regional economic
factors because of our geographic market concentration; (vi) increases in health insurance costs and workers compensation rates and underlying claims trends, health care reform, financial solvency of workers compensation carriers,
other insurers or financial institutions, state unemployment tax rates, liabilities for employee and client actions or payroll-related claims; (vii) failure to manage growth of our operations and the effectiveness of our sales and marketing
efforts; (viii) the impact of the competitive environment in the PEO industry on our growth and/or profitability; (ix) our liability for worksite employee payroll, payroll taxes and benefits costs; (x) our liability for disclosure of
sensitive or private information; (xi) our ability to integrate or realize expected returns on our acquisitions; (xii) failure of our information technology systems; (xiii) an adverse final judgment or settlement of claims against us;
and (xiv) disruptions to our business resulting from the actions of certain stockholders. These factors are discussed in further detail in our filings with the SEC. Any of these factors, or a combination of such factors, could materially affect
the results of our operations and whether forward-looking statements we make ultimately prove to be accurate.

Insperity, Inc. invites its stockholders to tender their common stock, par value $0.01 per share, of the Company for purchase by us. Upon the
terms and subject to the conditions of this Offer to Purchase and the Letter of Transmittal, we are offering to purchase shares of common stock pursuant to (i) Auction Tenders at prices specified by the tendering stockholders of not less than
$43.50 nor greater than $50.00 per share, or (ii) Purchase Price Tenders. We are offering to purchase shares having an aggregate Purchase Price of no more than $125 million.

The Offer will expire on January 7, 2016, at 5:00 p.m., New York City time, unless the Offer is extended or terminated by us.

After the Expiration Time, assuming the conditions to the Offer have been satisfied or waived, we will determine a single price per share, the
Purchase Price, which will be not less than $43.50 and not more than $50.00 per share, that we will pay for shares validly tendered in the Offer and not validly withdrawn, taking into account the number of shares tendered pursuant to Auction Tenders
and pursuant to Purchase Price Tenders and the prices specified by stockholders tendering shares pursuant to Auction Tenders. Shares tendered pursuant to Purchase Price Tenders will be deemed to have been tendered at a price of $43.50 per share
(which is the minimum price per share under the Offer) for purposes of determining the Purchase Price. The Purchase Price will be the lowest price per share of not less than $43.50 and not more than $50.00 per share at which shares have been
tendered or have been deemed to be tendered in the Offer that will enable us to purchase the maximum number of shares validly tendered in the Offer and not validly withdrawn having an aggregate purchase price not exceeding $125 million. Shares
validly tendered pursuant to an Auction Tender will not be purchased if the price specified in the Auction Tender is greater than the Purchase Price. All shares purchased pursuant to the Offer will be purchased at the same Purchase Price regardless
of whether the stockholder tendered at a lower price.

Only shares validly tendered at prices at or below the Purchase Price, and not
validly withdrawn, will be eligible for purchase. Shares tendered but not purchased pursuant to the Offer will be returned promptly following the Expiration Time. See Sections 3 and 4.

Unless tendering directly through DTC, stockholders must complete, among other items, the section of the Letter of Transmittal relating to the
price at which they are tendering shares in order to validly tender shares. Stockholders who validly tender shares without specifying whether they are making an Auction Tender or a Purchase Price Tender will be deemed to have made a Purchase Price
Tender. Any stockholder not tendering directly through DTC who wishes to tender shares at more than one price must complete a separate Letter of Transmittal for each price at which shares are being tendered. A stockholder tendering shares through
DTC using ATOP who wishes to tender shares at more than one price must complete a separate ATOP transfer with respect to the shares to be tendered at each price. The same shares cannot be tendered at more than one price, unless such shares have been
previously and validly withdrawn. See Sections 3 and 4.

The Offer is not conditioned upon any minimum number of shares being tendered.
The Offer is, however, subject to a number of other terms and conditions. See Section 7.

Our Board of Directors has approved
the Offer. However, none of our Board of Directors, the Dealer Manager, the Depositary or the Information Agent makes any recommendation to you as to whether to tender or refrain from tendering your shares or as to the price or prices at which you
may choose to tender your shares. We have not authorized any person to make any such recommendation. You must make your own decisions as to whether to tender your shares and, if so, how many shares to tender and the price or prices at which you will
tender them. In doing so, you should read carefully the information in, or incorporated by reference in, this Offer to Purchase and in the Letter of Transmittal, including the purposes and effects of the Offer. See Section 2. You are urged to
discuss your decisions with your own tax adviser, financial adviser and/or broker.

Upon the terms and subject to the conditions of the Offer, if shares having an aggregate purchase
price of $125 million or less are validly tendered and not validly withdrawn, we will buy all shares validly tendered and not validly withdrawn. Upon the terms and subject to the conditions of the Offer, if the number of shares of common stock
validly tendered at or below the Purchase Price and not validly withdrawn would result in an aggregate purchase price of more than $125 million, we will purchase shares:



First, from all holders of odd lots of less than 100 shares who validly tender all of their shares at or below the Purchase Price, and do not validly withdraw them (tenders of less than all of the
shares owned, beneficially or of record, by such odd lot shareholders will not qualify for this preference);



Second, from all other stockholders who validly tender shares at or below the Purchase Price, and do not validly withdraw them, on a pro rata basis, with appropriate adjustments to avoid the purchase of
fractional shares (except for stockholders who tendered shares conditionally for which the condition was not satisfied), until we have purchased shares resulting in an aggregate purchase price of $125 million; and



Third, only if necessary to permit us to purchase shares resulting in an aggregate purchase price of $125 million, from holders who validly tender shares at or below the Purchase Price (and do not validly
withdraw them) conditionally (for which the condition was not initially satisfied) by random lot, to the extent feasible. To be eligible for purchase by random lot, stockholders whose shares are conditionally tendered must have validly tendered and
not validly withdrawn all of their shares. See Sections 1 and 6.

Because of the odd lot priority, proration and
conditional tender provisions described above, we may not purchase all of the shares that you tender even if you tender them at or below the Purchase Price. See Section 1.

The Purchase Price will be paid to stockholders whose shares are accepted for payment in cash, less any applicable withholding taxes and
without interest. Tendering stockholders who hold shares registered in their own name and who tender their shares directly to the Depositary will not be obligated to pay brokerage commissions, solicitation fees or, except as set forth in
Section 5 hereof, stock transfer taxes on the purchase of shares by us pursuant to the Offer. Stockholders holding shares in a brokerage account or otherwise through a broker, dealer, commercial bank, trust company or other nominee are urged to
consult their broker, dealer, commercial bank, trust company or other nominee to determine whether any charges may apply if stockholders tender shares through such nominees and not directly to the Depositary. See Section 3.

Also, any tendering stockholder or other payee who is a U.S. Holder (as defined in Section 14) and who fails to complete, sign and
return to the Depositary, or other withholding agent, the Internal Revenue Service (IRS) Form W-9 included with the Letter of Transmittal and any tendering stockholder or other payee who is a Non-U.S. Holder (as defined in
Section 14) and who fails to complete, sign and return to the Depositary, or other withholding agent, the appropriate IRS Form W-8, may be subject to U.S. federal income tax backup withholding (currently at a rate of 28%) of the gross proceeds
paid to the stockholder or other payee pursuant to the Offer, unless such holder establishes that such holder is within the class of persons that is exempt from backup withholding. See Sections 3 and 14.

In addition, holders of vested but unexercised options to purchase shares of our common stock under our equity-based compensation plans may
exercise such options in accordance with the terms of our equity-based compensation plans and the Companys policies and practices, and tender in the Offer some or all of the shares issued upon such exercise. Holders of restricted stock awards
may not tender such restricted stock in the Offer unless and until such shares have vested and any other restrictions on such shares have lapsed. See Sections 3 and 11.

We will pay all reasonable fees and expenses incurred in connection with the Offer by Credit Suisse Securities (USA) LLC, the Dealer Manager
for the Offer, Innisfree M&A Incorporated, the Information Agent for the Offer, and Computershare Trust Company, N.A., the Depositary for the Offer. See Section 16.

As of December 1, 2015, there were 24,277,515 shares of our common stock issued and
outstanding. Since the Purchase Price will only be determined after the Expiration Time, the number of shares that will be purchased will not be known until after that time. Assuming that the Offer is fully subscribed, if the Purchase Price is
determined to be $43.50 per share, the minimum Purchase Price under the Offer, the approximate number of shares that will be purchased under the Offer is 2,873,563. Assuming that the Offer is fully subscribed, if the Purchase Price is determined to
be $50.00 per share, the maximum Purchase Price under the Offer, the approximate number of shares that will be purchased under the Offer is 2,500,000. Assuming that the Offer is fully subscribed, the maximum of 2,873,563 shares that the Company is
offering to purchase under the Offer represents approximately 11.8% of the total number of shares issued and outstanding as of December 1, 2015. Assuming the Offer is fully subscribed, the minimum of 2,500,000 shares that the Company is
offering to purchase under the Offer represents approximately 10.3% of the total number of shares issued and outstanding as of December 1, 2015. See Sections 1 and 11.

Our common stock is listed on the New York Stock Exchange and trades under the symbol NSP. On December 7, 2015, the
reported closing price of our common stock was $44.03 per share. The lower end of the price range for the Offer of $43.50 per share is below the closing market price on the NYSE for the shares of $44.03 on December 7, 2015, the last full trading day
before we commenced the Offer. You are urged to obtain current market quotations for our common stock before deciding whether, and at what price or prices, to tender your shares pursuant to the Offer. See Section 8.

General. Promptly following the
Expiration Time, Insperity will, upon the terms and subject to the conditions of the Offer, determine a single Purchase Price (which will be not less than $43.50 and not more than $50.00 per share) that it will pay for shares validly tendered in the
Offer and not validly withdrawn, taking into account the number of shares tendered pursuant to Auction Tenders and Purchase Price Tenders and the prices specified by stockholders tendering shares pursuant to Auction Tenders.

The Purchase Price will be the lowest price per share of not less than $43.50 and not more than $50.00 per share at which shares have been
tendered or have been deemed to be tendered in the Offer that will enable Insperity to purchase the maximum number of tendered shares having an aggregate purchase price not exceeding $125 million. Only shares validly tendered at prices at or below
the Purchase Price, and not validly withdrawn, will be eligible for purchase in the Offer. Shares validly tendered pursuant to an Auction Tender will not be purchased if the price specified in the Auction Tender is greater than the Purchase Price.

Promptly after determining the Purchase Price, Insperity will publicly announce the Purchase Price and all stockholders who have validly
tendered and not validly withdrawn their shares pursuant to Auction Tenders at prices equal to or less than the Purchase Price or pursuant to Purchase Price Tenders will receive the Purchase Price, payable in cash, without interest, but subject to
applicable withholding taxes, for all shares purchased upon the terms and subject to the conditions of the Offer, including the provisions relating to odd lot priority, proration and conditional tender described below.

Under a Purchase Price Tender, we will purchase shares, upon the terms and subject to the conditions of the Offer, at the Purchase
Price. If you wish to maximize the chance that we will purchase your shares in the Offer, you should validly tender your shares pursuant to a Purchase Price Tender. Shares tendered pursuant to Purchase Price Tenders will be deemed to have been
tendered at a price of $43.50 per share (which is the minimum price per share under the Offer) for purposes of determining the Purchase Price. Accordingly, Purchase Price Tenders could result in the Purchase Price being lower and could result in
your shares being purchased at the minimum price in the Offer.

Shares acquired pursuant to the Offer will be acquired by Insperity
free and clear of all liens, charges, encumbrances, security interests, claims, restrictions and equities whatsoever, together with all rights and benefits arising therefrom, provided that any dividends or distributions which may be declared, paid,
issued, distributed, made or transferred on or in respect of such shares to stockholders of record on or prior to the date on which the shares are purchased under the Offer shall be for the account of such stockholders. See Section 8.

The Offer is not conditioned upon any minimum number of shares being tendered. The Offer is, however, subject to a number of other terms
and conditions. See Section 7.

Priority of Purchases. Upon the terms and subject to the conditions of the Offer, if
shares having an aggregate purchase price of $125 million or less are validly tendered and not validly withdrawn, we will buy all shares validly tendered and not validly withdrawn. Upon the terms and subject to the conditions of the Offer, if the
number of shares validly tendered at or below the Purchase Price and not validly withdrawn would result in an aggregate purchase price of more than $125 million:



First, we will purchase all shares tendered by any Odd Lot Holder (as defined below) who:



validly tenders and does not validly withdraw all shares owned beneficially or of record by the Odd Lot Holder at a price at or below the Purchase Price (tenders of less than all of the shares owned by an Odd Lot Holder
will not qualify for this preference); and



completes the section entitled Odd Lots in the Letter of Transmittal or, in the case of a book-entry transfer, an Agents Message (as defined below), and, if applicable, in the Notice of Guaranteed
Delivery.

Second, subject to the conditional tender provisions described in Section 6, we will purchase all other shares validly tendered and not validly withdrawn at prices at or below the Purchase Price, on a pro
rata basis, with appropriate adjustments to avoid purchases of fractional shares, as described below, until we have purchased shares resulting in an aggregate purchase price of $125 million.



Third, only if necessary to permit us to purchase shares resulting in an aggregate purchase price of $125 million, shares conditionally tendered at or below the Purchase Price (for which the condition was not
initially satisfied) and not validly withdrawn, will, to the extent feasible, be selected for purchase by random lot. To be eligible for purchase by random lot, stockholders whose shares are conditionally tendered must have validly tendered and not
validly withdrawn all of their shares.

As a result of the foregoing priorities applicable to the purchase of shares
tendered, it is possible that all of the shares that a stockholder tenders in the Offer at or below the Purchase Price may not be purchased. In addition, if a tender is conditioned upon the purchase of a specified number of shares, it is possible
that none of those shares will be purchased.

Odd Lots. The term odd lots means all shares validly tendered
prior to the Expiration Time at prices at or below the Purchase Price and not validly withdrawn by any person who owned, beneficially or of record, a total of fewer than 100 shares and so certified in the appropriate place on the Letter of
Transmittal and, if applicable, on the Notice of Guaranteed Delivery (an Odd Lot Holder). To qualify for this preference, an Odd Lot Holder must tender all shares owned by the Odd Lot Holder in accordance with the procedures
described in Section 3. Odd lots will be accepted for payment before any proration of the purchase of other tendered shares. This preference is not available to partial tenders or to beneficial or record holders of 100 or more shares in the
aggregate, even if these holders have separate accounts or certificates representing fewer than 100 shares. By tendering in the Offer, an Odd Lot Holder who holds shares in his or her name and tenders such shares directly to the Depositary would not
only avoid the payment of brokerage commissions, but also would avoid any applicable odd lot discounts in a sale of the holders shares. Any Odd Lot Holder wishing to tender all of his or her shares pursuant to the Offer should complete the
section entitled Odd Lots in the Letter of Transmittal and, if applicable, in the Notice of Guaranteed Delivery.

Proration. The proration period is the period for accepting shares on a pro rata basis in the event that the Offer is over-subscribed.
The proration period will expire at the Expiration Time. If proration of tendered shares is required, we will determine the proration factor promptly following the Expiration Time. Subject to adjustment to avoid the purchase of fractional shares and
subject to conditional tenders described in Section 6, proration for each stockholder tendering shares at or below the Purchase Price (other than Odd Lot Holders) will be based on the ratio of the total number of shares to be purchased by us
(excluding shares purchased from Odd Lot Holders) to the number of shares validly tendered and not validly withdrawn by all stockholders (other than Odd Lot Holders) at or below the Purchase Price. This ratio will be applied to stockholders (other
than Odd Lot Holders) validly tendering shares at or below the Purchase Price to determine the number of shares that will be purchased from each tendering stockholder in the Offer. Because of the difficulty in determining the number of shares
validly tendered and not validly withdrawn, and because of the odd lot procedure described above and the conditional tender procedure described in Section 6, if the Offer is over-subscribed, we do not expect that we will be able to announce the
final proration factor or commence payment for any shares purchased pursuant to the Offer until up to four business days after the Expiration Time. The preliminary results of any proration will be announced by press release promptly after the
Expiration Time. After the Expiration Time, stockholders may obtain preliminary proration information from the Information Agent and also may be able to obtain the information from their brokers.

As described in Section 14, the number of shares that we will purchase from a stockholder pursuant to the Offer may affect the U.S.
federal income tax consequences of the purchase to the stockholder and, therefore, may

be relevant to a stockholders decisions whether or not to tender shares and whether or not to condition any tender upon our purchase of a stated number of shares held by such stockholder.
The Letter of Transmittal affords each stockholder who tenders shares registered in such stockholders name directly to the Depositary the opportunity to designate the order of priority in which shares tendered are to be purchased in the event
of proration as well as the ability to condition such tender on a minimum number of shares being purchased. See Section 6.

This
Offer to Purchase and the Letter of Transmittal will be mailed to record holders of the shares and will be furnished to brokers, dealers, commercial banks, trust companies and other nominee stockholders and similar persons whose names, or the names
of whose nominees, appear on Insperitys stockholder list or, if applicable, who are listed as participants in a clearing agencys security position listing for subsequent transmittal to beneficial owners of shares.

2.

Purpose of the Offer; Certain Effects of the Offer

Purpose of the Offer. Our
Board of Directors, with the assistance of management, has decided to conduct the Offer after reviewing a variety of alternatives for using our available financial resources. Our Board considered our existing and anticipated capitalization and
financial position, including our outstanding common stock, liquidity, cash position, working capital, our lack of long-term debt, and our operations, strategy and expectations for the future.

The Board believes that the Offer represents a prudent use of our financial resources in light of our business profile, assets, current
indebtedness and debt capacity. At September 30, 2015, we had working capital of $76.4 million, no long-term debt and $124.4 million of available borrowing capacity under our existing revolving credit facility. The primary purpose of the
Offer is to return cash to our stockholders by providing them with the opportunity to tender all or a portion of their shares and, thereby, receive a return of some or all of their investment if they so elect. In addition, if we complete the Offer,
stockholders who do not participate in the Offer will automatically increase their relative percentage ownership interest in us and our future operations.

Assuming the Offer is fully subscribed, we believe that our anticipated cash flow from operations, our access to credit and capital markets
and our financial condition will be adequate for our needs. However, actual experience may differ significantly from our expectations. See Forward-Looking Statements. In considering the Offer, our management and our Board of Directors
took into account the expected financial impact of the Offer on our liquidity.

Where shares are tendered by the registered owner of those
shares directly to the Depositary, the sale of those shares in the Offer may permit the seller to avoid the usual transaction costs associated with open market sales. Furthermore, any Odd Lot Holders who hold shares registered in their names and
tender their shares directly to the Depositary and whose shares are purchased under the Offer will avoid not only the payment of brokerage commissions but also any applicable odd lot discounts that might be payable on sales of their shares in market
transactions.

In addition, stockholders who wish to achieve a greater percentage of equity ownership in the Company will be able to do so
by not tendering their shares in the Offer, and, if the Company completes the Offer, will therefore have a greater percentage ownership in Insperity and its future earnings and assets, while also bearing the attendant risks associated with owning
the Companys common stock.

After the completion or termination of the Offer, we may purchase additional shares in the open market
subject to market conditions. We may also purchase shares in private transactions, tender offers or otherwise. Any of these purchases may be on the same terms as, or on terms more or less favorable to stockholders than, the terms of the Offer.
However, Rule 13e-4 under the Exchange Act generally prohibits us and our affiliates from

purchasing any shares, other than through the Offer, until at least 10 business days after the expiration or termination of the Offer. Any possible future purchases by us will depend on many
factors, including the market price of the shares, the results of the Offer, our business and financial position and general economic and market conditions.

Although our Board of Directors has approved the Offer, none of our Board of Directors, the Dealer Manager, the Information Agent or the
Depositary has made, or is making, any recommendation to you as to whether to tender or refrain from tendering your shares or as to the price or prices at which you may choose to tender your shares. We have not authorized any person to make any such
recommendation. You must make your own decisions as to whether to tender your shares and, if so, how many shares to tender and the price or prices at which you will tender them. In doing so, you should read carefully the information in, or
incorporated by reference in, this Offer to Purchase and in the Letter of Transmittal, including the purposes and effects of the offer. You are urged to discuss your decisions with your own tax adviser, financial adviser and/or broker.

Certain Effects of the Offer. Stockholders who do not tender their shares in the Offer and stockholders who otherwise retain an equity
interest in the Company as a result of a partial tender of shares or proration will continue to be owners of the Company and be subject to the risks of such ownership. If we complete the Offer, those stockholders will realize an automatic increase
in their relative ownership interest in the Company and also will bear the attendant risks associated with the increased ownership interest. Stockholders may be able to sell non-tendered shares in the future at a net price significantly higher or
lower than the Purchase Price pursuant to the Offer. We can give no assurance as to the price at which a stockholder may be able to sell its shares in the future.

The Offer will reduce our public float (the number of shares of our common stock owned by non-affiliated stockholders and
available for trading in the securities markets), and is likely to reduce the number of our stockholders. This may result in lower stock prices or reduced liquidity in the trading market for our shares in the future.

Our directors and executive officers have advised us that they do not intend to tender shares in the Offer. We are not aware of any of our
affiliates that intend to tender any shares in the Offer. In addition, Starboard, which owned approximately 13.74% of our shares as of December 1, 2015, has advised us that it does not intend to participate in the Offer. The equity ownership of
our directors and executive officers will proportionately increase as a percentage of our outstanding common stock following the consummation of the Offer. Our directors and executive officers may, subject to applicable law and applicable policies
and practices of the Company, sell their shares from time to time in open market transactions at prices that may be more or less favorable than the Purchase Price to be paid to our stockholders pursuant to the Offer. See Section 11.

Based on the published guidelines of the NYSE and the conditions of the Offer, we believe that our purchase of shares pursuant to the Offer
will not result in delisting of the remaining shares on the NYSE. Our common stock is registered under the Exchange Act, which requires, among other things, that we furnish certain information to our stockholders and the SEC and comply with the
SECs proxy rules in connection with meetings of our stockholders. We believe that our purchase of shares pursuant to the Offer will not result in the shares becoming eligible for termination of registration under the Exchange Act. The Offer is
conditioned upon, among other things, our having determined that the consummation of the Offer will not cause the shares to be delisted from the NYSE or to be eligible for deregistration under the Exchange Act. See Section 7.

Shares acquired pursuant to the Offer will be retired and returned to the status of authorized but unissued stock of the Company and will be
available to us without further stockholder action, except as required by applicable law or the rules of the NYSE or any securities exchange on which the shares are then listed, for purposes including, without limitation, the acquisition of other
businesses, the raising of additional capital for use in our business and the satisfaction of obligations under existing or future employee benefit or compensation programs or stock plans or compensation programs for directors. We have no current
plans for the shares purchased in the Offer.

Our shares are currently margin securities under the rules of the Federal Reserve
Board. This has the effect, among other things, of allowing brokers to extend credit to their customers using the shares as collateral. We believe that, following the purchase of shares pursuant to the Offer, the shares will continue to be
margin securities for purposes of the Federal Reserve Boards margin regulations.

Other Plans or Proposals.
Except as disclosed or incorporated by reference in this Offer to Purchase, Insperity currently has no plans, proposals or negotiations that relate to or would result in:

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any extraordinary transaction, such as a merger, reorganization or liquidation, involving Insperity or any of its subsidiaries;

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any purchase, sale or transfer of a material amount of assets of Insperity or any of its subsidiaries;



any material change in the present dividend policy, or indebtedness or capitalization of Insperity;

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any change in the present Board of Directors or management of Insperity, including, but not limited to, any plans or proposals to change the number or the term of directors or to fill any existing vacancies on the Board
or to change any material term of the employment contract of any executive officer;

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any other material change in Insperitys corporate structure or business;



any class of equity securities of Insperity becoming eligible for termination of registration under Section 12(g)(4) of the Exchange Act or ceasing to be authorized for listing on the NYSE;

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the suspension of Insperitys obligation to file reports under Section 15(d) of the Exchange Act;

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the acquisition by any person of additional securities of Insperity, or the disposition by any person of securities of Insperity, other than purchases pursuant to outstanding options to purchase shares and outstanding
restricted stock awards granted to certain employees (including directors and officers); or



any changes in Insperitys Certificate of Incorporation, Amended and Restated Bylaws or other governing instruments or other actions that, in each case, could impede the acquisition of control of Insperity.

On March 21, 2015, we entered into an agreement with Starboard and certain of its affiliates pursuant to which Peter A.
Feld, Norman R. Sorensen and Michelle McKenna-Doyle became members of our Board of Directors. In addition, Starboard agreed that until the earlier of (i) 15 business days prior to the deadline for the submission of stockholder nominations for the
2016 Annual Meeting pursuant to the Companys Amended and Restated Bylaws and (ii) the date that is 100 days prior to the first anniversary of the 2015 Annual Meeting (the Standstill Period), it would not solicit proxies
regarding any matter to come before any annual or special meeting of stockholders, including for the election of directors, or enter into a voting agreement or any group with shareholders other than Starboard affiliates and current group members. In
addition, among other standstill provisions, Starboard agreed that, during the Standstill Period, Starboard will not seek to make, or encourage any third party in making, any offer or proposal with respect to any merger, acquisition,
recapitalization, restructuring, disposition or other business combination involving the Company and will not seek, or encourage any person, to submit nominees in furtherance of a contested solicitation for the election or removal of directors. The
Standstill Period will expire on February 22, 2016. We occasionally have discussions with Starboard concerning the agreement and expect to have additional discussions prior to the expiration of the Standstill Period, including concerning the
expiration of the Standstill Period, the size and composition of our Board of Directors and potential actions that Starboard may take following the expiration of the Standstill Period.

Although we do not currently have any plans, other than as disclosed or incorporated by reference in this Offer to Purchase, that relate to or
would result in any of the events discussed above, as we evaluate opportunities, we may undertake or plan actions that relate to or could result in one or more of these events. We reserve the right to change our plans and intentions at any time as
we deem appropriate.

Valid Tender of Shares. For shares to be
tendered validly in the Offer:

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the certificates for shares of our common stock, or confirmation of receipt of the shares pursuant to the procedure for book-entry transfer set forth below, together with a validly completed and duly executed Letter of
Transmittal, including any required signature guarantees, or an Agents Message in the case of a book-entry transfer, and any other documents required by the Letter of Transmittal, must be received prior to the Expiration Time by the Depositary
at its address set forth on the back cover page of this Offer to Purchase; or



the tendering stockholder must, prior to the Expiration Time, comply with the guaranteed delivery procedure set forth below.

In accordance with Instructions 4 and 5 to the Letter of Transmittal, each stockholder who is not tendering through DTC and who desires to
tender shares in the Offer must either check (1) one, and only one, of the boxes in the section of the Letter of Transmittal captioned Auction Price Tender: Price (in Dollars) per Share at Which Shares are Being Tendered, indicating
the price (in increments of $0.25) at which shares are being tendered, or (2) the box in the section of the Letter of Transmittal captioned Purchase Price Tender, in which case you will be deemed to have tendered your shares at the
minimum price of $43.50 per share. You should understand that this election may cause the Purchase Price to be lower and could result in the tendered shares being purchased at the minimum price of $43.50 per share, a price that is below the closing
market price on the NYSE for the shares of $44.03 on December 7, 2015, the last full trading day before we commenced the Offer. A tender of shares not being made through DTC using ATOP will be proper only if, among other things, one, and only
one, of these boxes is checked on the Letter of Transmittal. Stockholders who validly tender shares without specifying whether they are making an Auction Tender or Purchase Price Tender will be deemed to have made a Purchase Price Tender.

If tendering stockholders wish to maximize the chance that we will purchase their shares, they should check the box in the section of
the Letter of Transmittal captioned Purchase Price Tender. Shares tendered pursuant to Purchase Price Tenders will be deemed to have been tendered at a price of $43.50 per share (which is the minimum price per share under the Offer) for
purposes of determining the Purchase Price. Accordingly, Purchase Price Tenders could result in the Purchase Price being lower and could result in your shares being purchased at the minimum price in the Offer. See Section 8 for recent market
prices for shares of our common stock.

If tendering stockholders using a Letter of Transmittal wish to indicate a specific price (in
increments of $0.25) at which their shares are being tendered, they must check the box indicating such price under the section captioned Auction Price Tenders: Price (in Dollars) per Share at Which Shares are Being Tendered. Tendering
stockholders should be aware that this election could result in none of their shares being purchased if the Purchase Price selected by the Company for the shares is less than the price selected by the stockholder. A stockholder not tendering
directly through DTC using ATOP who wishes to tender shares at more than one price must complete a separate Letter of Transmittal for each price at which shares are being tendered. A stockholder tendering shares through DTC using ATOP who wishes to
tender shares at more than one price must complete a separate ATOP transfer with respect to the shares to be tendered at each price. The same shares cannot be tendered (unless previously validly withdrawn in accordance with the terms of the Offer)
at more than one price. Separate notices of withdrawal (described in Section 4) are not required for each Letter of Transmittal unless each Letter of Transmittal tenders shares at different prices; however, absent a notice of withdrawal,
subsequent Letters of Transmittal do not revoke prior Letters of Transmittal. Stockholders may contact the Depositary for additional instructions.

Stockholders holding shares in a brokerage account or otherwise through a broker, dealer, commercial bank, trust company or other nominee,
must contact their broker, dealer, commercial bank, trust company or other

nominee in order to tender their shares. Stockholders who hold shares through nominee stockholders are urged to consult their nominees to determine whether any charges may apply if stockholders
tender shares through such nominees and not directly to the Depositary.

Odd Lot Holders must tender all of their shares and also complete
the section entitled Odd Lots in the Letter of Transmittal and, if applicable, in the Notice of Guaranteed Delivery, if they wish to qualify for the preferential treatment available to Odd Lot Holders as described in Section 1.

Stockholders may tender shares subject to the condition that all or a specified minimum number of shares be purchased. Any stockholder
desiring to make such a conditional tender should so indicate in the section entitled Conditional Tender in the Letter of Transmittal and, if applicable, in the Notice of Guaranteed Delivery. It is the tendering stockholders
responsibility to determine the minimum number of shares to be purchased. Stockholders are urged to consult their own investment and tax advisers with respect to the effect of proration of the Offer and the advisability of making a conditional
tender. See Sections 6 and 14.

Signature Guarantees and Method of Delivery. If a certificate for shares of our common stock is
registered in the name of a person other than the person executing a Letter of Transmittal, or if payment is to be made, or shares not purchased or tendered are to be issued to a person other than the registered holder of the certificatesurrendered, then the tendered certificate must be endorsed or accompanied by an appropriate stock power, signed in either case exactly as the name of the registered holder appears on the certificate, with the signature guaranteed by an Eligible
Institution (as defined below). No signature guarantee is required if:

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the Letter of Transmittal is signed by the registered holder of the shares tendered and the holder has not completed either the box entitled Special Delivery Instructions or the box entitled Special
Payment Instructions in the Letter of Transmittal; or



shares are tendered for the account of a broker, dealer, commercial bank, credit union, savings association or other entity which is a member in good standing of the Securities Transfer Agents Medallion Program or a
broker, dealer, commercial bank, credit union, savings association or other entity that is also an eligible guarantor institution, as the term is defined in Rule 17Ad-15 under the Exchange Act (each of the foregoing constituting an
Eligible Institution).

In all cases, payment for shares tendered and accepted for payment pursuant to the Offer
will be made only after timely receipt by the Depositary of certificates for the shares (or a timely confirmation of the book-entry transfer of the shares into the Depositarys account at DTC, as described below), a validly completed and duly
executed Letter of Transmittal, including any required signature guarantees, or an Agents Message (as defined below) in the case of a book-entry transfer, and any other documents required by the Letter of Transmittal.

The method of delivery of all documents, including certificates for shares of our common stock, the Letter of Transmittal and any other
required documents, including delivery through DTC, is at the sole election and risk of the tendering stockholder. Shares will be deemed delivered only when actually received by the Depositary (including, in the case of a book-entry transfer, by
book-entry confirmation). If delivery is by mail, then registered mail with return receipt requested, validly insured, is recommended. In all cases, sufficient time should be allowed to ensure timely delivery.

All deliveries made in connection with the Offer, including a Letter of Transmittal and certificates for shares, must be made to the
Depositary and not to us, the Dealer Manager, the Information Agent or DTC. Any documents delivered to us, the Dealer Manager, the Information Agent or DTC will not be forwarded to the Depositary and therefore will not be deemed to be validly
tendered.

Book-Entry Delivery. The Depositary will establish an account with respect to the shares for purposes of the Offer
at DTC within two business days after the date of this Offer to Purchase, and any financial institution that is a participant in DTCs system may make book-entry delivery of the shares by causing DTC to transfer those

shares into the Depositarys account in accordance with DTCs procedures for that transfer. Although delivery of shares may be effected through a book-entry transfer into the
Depositarys account at DTC, either (1) a validly completed and duly executed Letter of Transmittal, with any required signature guarantees, or an Agents Message, and any other required documents must, in any case, be transmitted to, and
received by, the Depositary at its address set forth on the back cover page of this Offer to Purchase prior to the Expiration Time or (2) the guaranteed delivery procedure described below must be followed if book-entry transfer of the shares
cannot be effected prior to the Expiration Time.

The confirmation of a book-entry transfer of shares into the Depositarys
account at DTC is referred to in this Offer to Purchase as a book-entry confirmation. Delivery of documents to DTC in accordance with DTCs procedures will not constitute delivery to the Depositary.

The term Agents Message means a message transmitted by DTC to, and received by, the Depositary and forming a
part of a book-entry confirmation, which states that DTC has received an express acknowledgement from the participant tendering shares through DTC that such participant has received, and agrees to be bound by, the terms of the Letter of Transmittal
and that Insperity may enforce such agreement against that participant.

Guaranteed Delivery. If a stockholder desires to
tender shares in the Offer and the stockholders stock certificates are not immediately available or cannot be delivered to the Depositary prior to the Expiration Time(or the procedures for book-entry transfer cannot be completed on a
timely basis), or if time will not permit delivery of all required documents to the Depositary prior to the Expiration Time, the shares may still be tendered if all of the following conditions are satisfied:

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the tender is made by or through an Eligible Institution;

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the Depositary receives by mail, overnight courier or facsimile transmission, prior to the Expiration Time, a validly completed and duly executed Notice of Guaranteed Delivery in the form we have provided with this
Offer to Purchase, including (where required) a signature guarantee by an Eligible Institution in the form set forth in the Notice of Guaranteed Delivery; and



the certificates for all tendered shares, in proper form for transfer (or confirmation of book-entry transfer of the shares into the Depositarys account at DTC), together with a validly completed and duly executed
Letter of Transmittal, or an Agents Message in the case of a book-entry transfer, and any required signature guarantees and other documents required by the Letter of Transmittal, are received by the Depositary within three business days after
the date of receipt by the Depositary of the Notice of Guaranteed Delivery.

Stockholders may contact the Information Agent,
the Dealer Manager or their broker, dealer, commercial bank, trust company or other nominee for assistance. The contact information for the Information Agent and the Dealer Manager is on the back cover page of this Offer to Purchase.

Stock Options. Options to purchase shares of our common stock cannot be tendered in the Offer. If you hold vested but unexercised
options, you may exercise such options in accordance with the terms of our equity-based compensation plans and the Companys policies and practices, and tender the shares received upon such exercise in accordance with the Offer. Exercises of
options cannot be revoked even if some or all of the shares received upon the exercise thereof and tendered in the Offer are not purchased pursuant to the Offer for any reason. You should evaluate this Offer to Purchase carefully to determine if
participation would be advantageous to you based on your stock option exercise prices and the expiration date of your options, the range of tender prices and the provisions for pro rata purchases by Insperity described in Section 1. We strongly
encourage optionholders to discuss the Offer with their own tax advisers, financial advisers and/or brokers.

Please be advised
that it is the optionholders responsibility to tender shares in the Offer to the extent such holder wants to participate and it may be difficult to secure delivery of shares issued pursuant to the exercise of

vested stock options in a time period sufficient to allow tender of those shares prior to the Expiration Time. Accordingly, we suggest that you exercise your vested options and satisfy the
exercise price for such shares in accordance with the terms of the related stock option plan and option agreement and Company policies and practices at least five business days prior to the date on which the Expiration Time is initially schedule to
occur (which, unless the Offer is extended, means you should exercise your vested stock options and satisfy the related exercise price no later than 5:00 p.m., New York City time, on December 30, 2015). Exercises of options cannot be revoked
even if some or all of the shares received upon the exercise thereof and tendered in the Offer are not purchased pursuant to the Offer for any reason.

Restricted Stock Awards. Holders of restricted stock awards under our equity-based compensation plans may not tender the shares
underlying such restricted stock awards in the Offer unless and until such shares have vested and any other restrictions on the restricted stock awards have lapsed. If the restrictions on the restricted stock awards have lapsed, you may tender some
or all of such shares in the Offer. See  Valid Tender of Shares above.

Return of Unpurchased Shares. If
any tendered shares are not purchased, or if less than all shares evidenced by a stockholders certificates are tendered, a Direct Registration Book-Entry Statement for unpurchased shares will be returned promptly after the expiration or
termination of the Offer or the valid withdrawal of the shares, or, in the case of shares tendered by book-entry transfer at DTC, the shares will be credited to the appropriate account maintained by the tendering stockholder at DTC, in each case
without expense to the stockholder.

U.S. Federal Income Tax Backup Withholding. Under the U.S. federal income tax backup
withholding rules, a portion (28% under current law) of the gross proceeds payable to a stockholder or other payee pursuant to the Offer may be withheld and remitted to the IRS, unless the stockholder or other payee (i) establishes that it is
an exempt recipient (as described below) or (ii) provides its taxpayer identification number (employer identification number or social security number) to the Depositary, or other withholding agent (as payer), as well as certain
other information and certifies under penalties of perjury that the number is correct, the stockholder is a U.S. person and the stockholder is not subject to backup withholding. Therefore, each tendering stockholder that is a U.S. Holder (as defined
in Section 14) should complete and sign the IRS Form W-9 included as part of the Letter of Transmittal so as to provide the information and certification necessary to avoid backup withholding unless the stockholder otherwise establishes to the
satisfaction of the Depositary, or other withholding agent, that the stockholder is not subject to backup withholding. If a U.S. Holder does not provide the Depositary, or other withholding agent, with the correct taxpayer identification number, the
U.S. Holder may be subject to penalties imposed by the IRS. If backup withholding results in an overpayment of taxes, a refund may be obtained from the IRS in accordance with its refund procedures. Certain exempt recipients (including,
among others, generally all corporations and certain Non-U.S. Holders (as defined in Section 14)) are not subject to backup withholding. In order for a Non-U.S. Holder to qualify as an exempt recipient, that stockholder must submit an
appropriate IRS Form W-8, signed under penalties of perjury, attesting to that stockholders exempt status. This statement can be obtained from the IRS website at www.irs.gov. See Instruction 3 of the related Letters of Transmittal.

To prevent U.S. federal income tax backup withholding, each stockholder that is a U.S. Holder and does not otherwise establish an
exemption from backup withholding should provide the Depositary, or other withholding agent, with the stockholders correct taxpayer identification number and provide other information by completing the IRS Form W-9 included as part of the
Letter of Transmittal, and each Non-U.S. Holder which does not otherwise establish an exemption from backup withholding must provide the Depositary, or other withholding agent, with the appropriate IRS Form W-8, which can be obtained from the IRS
website at www.irs.gov.

For a discussion of U.S. federal income tax consequences to tendering stockholders, see
Section 14.

Withholding for Non-U.S. Holders. Even if a Non-U.S. Holder has provided the required certification to avoid
backup withholding, the Depositary, or other withholding agent, will withhold an amount equal to 30% of the gross payments payable to the Non-U.S. Holder or his agent unless (a) the Depositary, or other withholding agent, determines that a
reduced rate of withholding is available under a tax treaty or (b) an exemption from withholding is applicable because the gross proceeds are effectively connected with the conduct of a trade or business within the U.S. (and, if a treaty
applies, the gross proceeds are attributable to a U.S. permanent establishment or fixed base maintained by such Non-U.S. Holder) See Section 14.

To obtain a reduced rate of withholding under a tax treaty, a Non-U.S. Holder must deliver to the Depositary, or other withholding agent, a
validly completed and executed IRS Form W-8BEN or IRS Form W-8BEN-E, as applicable. To obtain an exemption from withholding on the grounds that the gross proceeds paid pursuant to the Offer are effectively connected with the conduct of a trade or
business within the United States, a Non-U.S. Holder must deliver to the Depositary, or other withholding agent, a validly completed and executed IRS Form W-8ECI. The Depositary, or other withholding agent, will determine a stockholders status
as a Non-U.S. Holder and eligibility for a reduced rate of, or exemption from, withholding by reference to any outstanding, valid certificates or statements concerning eligibility for a reduced rate of, or exemption from, withholding unless facts
and circumstances indicate that reliance is not warranted.

A Non-U.S. Holder may be eligible to obtain a refund of all or a portion of
any amount withheld if (a) the Non-U.S. Holder meets the complete termination, substantially disproportionate or not essentially equivalent to a dividend tests described in Section 14 that would
characterize the transaction as an exchange (as opposed to a distribution) with respect to which the Non-U.S. Holder is not subject to tax, or (b) is otherwise able to establish that no tax or a reduced amount of tax is due.

Non-U.S. Holders are advised to consult their own tax advisers regarding the application of U.S. federal income tax withholding, including
eligibility for a withholding rate reduction or exemption, and the refund procedure.

FATCA Withholding. FATCA (as defined in
Section 14) generally imposes a U.S. federal withholding tax of 30% on dividend income from our shares if paid to a foreign financial institution or a non-financial foreign entity (each as defined in the Code)
(including, in some cases, when such foreign financial institution or non-financial foreign entity is acting as an intermediary for the beneficial owner), unless those entities comply with a complicated U.S. information reporting, disclosure and
certification regime. As described above, the Depositary, or other withholding agent, generally will treat amounts paid pursuant to the Offer as a dividend, and, therefore, such amounts may be subject to FATCA withholding. If the Depositary, or
other withholding agent, withholds tax under FATCA, it will not also withhold the 30% U.S. federal income tax described above.

Stockholders are advised to consult their own tax advisers regarding the possible impact FATCA may have on an exchange of shares for cash
pursuant to the Offer.

Determination of Validity; Rejection of Shares; Waiver of Defects; No Obligation to Give Notice of
Defects. All questions as to the number of shares to be accepted, the Purchase Price to be paid for shares to be accepted and the validity, form, eligibility, including time of receipt, and acceptance for payment of any tender of shares will be
determined by us, in our sole discretion and will be final and binding on all parties absent a finding to the contrary by a court of competent jurisdiction. We reserve the absolute right to reject any or all tenders of any shares that we determine
are not in proper form or the acceptance for payment of or payment for which we determine may be unlawful. We also reserve the absolute right to waive any of the conditions of the Offer prior to the Expiration Time with respect to all tendered
shares. We also reserve the absolute right to waive any defect or irregularity in any tender with respect to any particular shares, whether or not we waive similar defects or irregularities in the case of any other stockholder. No tender of shares
will be deemed to have been validly made

until all defects or irregularities have been cured by the tendering stockholder or waived by us. We will not be liable for failure to waive any condition of the Offer, or any defect or
irregularity in any tender of shares. None of us, the Depositary, the Information Agent, the Dealer Manager or any other person will be obligated to give notice of any defects or irregularities in tenders, nor will any of them incur any liability
for failure to give any such notice.

Tendering Stockholders Representation and Warranty; Our Acceptance Constitutes an
Agreement. It is a violation of Rule 14e-4 promulgated under the Exchange Act for a person acting alone or in concert with others, directly or indirectly, to tender shares for such persons own account unless, at the time of tender and at
the end of the proration period or period during which shares are accepted by lot, such person has a net long position (i.e., more shares held in long positions than in short positions) in (1) a number of shares that is equal to or
greater than the amount tendered and will deliver or cause to be delivered such shares for the purpose of tendering to us within the period specified in the Offer or (2) other securities immediately convertible into, exercisable for or
exchangeable into a number of shares (Equivalent Securities) that are equal to or greater than the number of shares tendered and, upon the acceptance of such tender, will acquire such shares by conversion, exchange, or exercise of
such Equivalent Securities and will deliver or cause to be delivered such shares so acquired for the purpose of tender to us within the period specified in the Offer. Rule 14e-4 also provides a similar restriction applicable to the tender or
guarantee of a tender on behalf of another person. A tender of shares made pursuant to any method of delivery set forth herein will constitute the tendering stockholders acceptance of the terms and conditions of the Offer, as well as the
tendering stockholders representation and warranty to us that (i) such stockholder has a net long position in a number of shares or Equivalent Securities at least equal to the shares being tendered within the meaning of Rule
14e-4 and (ii) such tender of shares complies with Rule 14e-4. Our acceptance for payment of shares tendered in the Offer will constitute a binding agreement between the tendering stockholder and us upon the terms and subject to the conditions
of the Offer, which agreement will be governed by, and construed in accordance with, the laws of the State of New York.

Lost or
Destroyed Certificates. If any certificate representing shares of our common stock has been lost or destroyed, the stockholder should promptly notify the Depositary at the phone number or address set forth on the back cover page of this Offer to
Purchase. The Letter of Transmittal and related documents cannot be processed until the procedures for replacing lost or destroyed certificates have been followed. Stockholders are requested to contact the Depositary immediately in order to permit
timely processing of this documentation.

Certificates for shares, together with a validly completed Letter of Transmittal and
any other documents required by the Letter of Transmittal, must be delivered to the Depositary and not to Insperity or the Information Agent. Any certificates delivered to Insperity, the Dealer Manager, the Information Agent or DTC will not be
forwarded to the Depositary and will not be deemed to be validly tendered.

4.

Withdrawal Rights

Shares tendered in the Offer may be withdrawn at any time prior to
the Expiration Time. In addition, unless Insperity has already accepted your tendered shares for payment, you may withdraw your tendered shares at any time after 11:59 p.m., New York City time, on February 9, 2016. Except as otherwise provided
in this Section 4, tenders of shares pursuant to the Offer are irrevocable.

For a withdrawal to be effective, a written or facsimile
notice of withdrawal must be received in a timely manner, as described in the immediately preceding paragraph, by the Depositary at its address set forth on the back cover page of this Offer to Purchase, and any notice of withdrawal must specify the
name of the tendering stockholder, the number of shares to be withdrawn, the price at which such shares were tendered, if an Auction Tender is being withdrawn, and the name of the registered holder of the shares to be withdrawn, if different from
the person who tendered the shares. A stockholder who has tendered shares at more than one price must complete a separate notice of withdrawal for shares tendered at each price. If the certificates for shares to be withdrawn have been delivered or
otherwise identified to the Depositary, then, before the release of those certificates, the

tendering stockholder also must submit the serial numbers shown on those particular certificates for shares to be withdrawn and, unless an Eligible Institution has tendered those shares, the
signature(s) on the notice of withdrawal must be guaranteed by an Eligible Institution. If shares have been tendered pursuant to the procedure for book-entry transfer described in Section 3, the notice of withdrawal also must specify the name
and the number of the account at DTC to be credited with the withdrawn shares and must otherwise comply with DTCs procedures.

All
questions as to the form and validity, including the time of receipt, of any notice of withdrawal will be determined by Insperity, in its sole discretion and will be final and binding on all parties absent a finding to the contrary by a court of
competent jurisdiction. We reserve the absolute right to waive any defect or irregularity in the notice of withdrawal or method of withdrawal of shares by any stockholder, whether or not we waive similar defects or irregularities in the case of any
other stockholder. None of us, the Depositary, the Information Agent, the Dealer Manager or any other person will be obligated to give notice of any defects or irregularities in any notice of withdrawal, nor will any of them incur liability for
failure to give any such notice.

Withdrawals may not be rescinded, and any shares validly withdrawn will be deemed not validly tendered
for purposes of the Offer. However, validly withdrawn shares may be re-tendered prior to the Expiration Time by again following one of the procedures described in Section 3.

If we extend the Offer, is delayed in its purchase of shares, or is unable to purchase shares pursuant to the Offer for any reason, then,
without prejudice to our rights under the Offer, the Depositary may, subject to applicable law, retain tendered shares on our behalf, and such shares may not be withdrawn, except to the extent tendering stockholders are entitled to withdrawal rights
as described in this Section 4 (subject to Rule 13e-4(f)(5) under the Exchange Act, which provides that the issuer making the Offer shall either pay the consideration offered, or return the tendered securities promptly after the termination of
the Offer).

5.

Purchase of Shares and Payment of Purchase Price

Upon the terms and subject to the
conditions of the Offer, promptly following the Expiration Time, we will (1) determine the Purchase Price we will pay for shares validly tendered and not validly withdrawn, taking into account the number of shares so tendered and the prices
specified by tendering stockholders and (2) accept for payment and pay an aggregate purchase price of up to $125 million for shares that are validly tendered at prices at or below the Purchase Price and not validly withdrawn. For purposes of
the Offer, we will be deemed to have accepted for payment, subject to the odd lot priority, proration and conditional tender provisions of the Offer, shares that are validly tendered at or below the Purchase Price and not validly
withdrawn, only when, as and if we give oral or written notice to the Depositary of our acceptance of the shares for payment pursuant to the Offer.

Upon the terms and subject to the conditions of the Offer, we will accept for payment and pay the Purchase Price per share for all of the
shares accepted for payment pursuant to the Offer promptly after the Expiration Time. In all cases, payment for shares tendered and accepted for payment pursuant to the Offer will be made promptly, taking into account any time necessary to determine
any proration, but only after timely receipt by the Depositary of (1) certificates for shares, or a timely book-entry confirmation of the deposit of shares into the Depositarys account at DTC, (2) a validly completed and duly
executed Letter of Transmittal including any required signature guarantees, or, in the case of a book-entry transfer, an Agents Message, and (3) any other required documents.

We will pay for shares purchased pursuant to the Offer by depositing the aggregate purchase price for the shares with the Depositary, which
will act as agent for tendering stockholders for the purpose of receiving payment from us and transmitting payment to the tendering stockholders.

In the event of proration, we will determine the proration factor and pay for those tendered shares accepted for payment promptly after the
Expiration Time. However, we do not expect to be able to announce the final

results of any proration or commence payment for any shares purchased pursuant to the Offer until up to four business days after the Expiration Time. A Direct Registration Book-Entry Statement
for all shares tendered and not purchased, including all shares tendered at prices in excess of the Purchase Price and shares not purchased due to proration or conditional tenders, will be returned or, in the case of shares tendered by book-entry
transfer, will be credited to the account maintained with DTC by the participant who delivered the shares, to the tendering stockholder at our expense promptly after the Expiration Time or termination of the Offer.

Under no circumstances will we pay interest on the Purchase Price, even if there is any delay in making payment. In addition, if certain
events occur prior to the Expiration Time, we may not be obligated to purchase shares pursuant to the Offer. See Section 7.

We
will pay all stock transfer taxes, if any, payable on the transfer to us of shares purchased pursuant to the Offer. If, however, payment of the Purchase Price is to be made to, or (in the circumstances permitted by the Offer) if unpurchased shares
are to be registered in the name of, any person other than the registered holder, or if tendered certificates are registered in the name of any person other than the person signing the Letter of Transmittal, the amount of all stock transfer taxes,
if any (whether imposed on the registered holder or the other person), payable on account of the transfer to the person, will be deducted from the Purchase Price unless satisfactory evidence of the payment of the stock transfer taxes, or exemption
from payment of the stock transfer taxes, is submitted to the Depositary.

6.

Conditional Tender of Shares

Under certain circumstances described in Section 1
and subject to the exception for Odd Lot Holders, if the Offer is over-subscribed, we will prorate the shares purchased pursuant to the Offer. As discussed in Section 14, the number of shares to be purchased from a particular stockholder may
affect the U.S. federal income tax treatment of the purchase to the stockholder and the stockholders decision whether to tender. The conditional tender alternative is made available for stockholders seeking to take steps to have payment for
shares sold pursuant to the Offer treated as received in a sale or exchange of such shares by the stockholder, rather than as a distribution to the stockholder, for U.S. federal income tax purposes. Accordingly, a stockholder may tender shares
subject to the condition that all or a specified minimum number of the stockholders shares tendered must be purchased if any shares tendered are purchased. Any stockholder desiring to make a conditional tender must so indicate in the section
entitled Conditional Tender in the Letter of Transmittal, and, if applicable, in the Notice of Guaranteed Delivery. It is the tendering stockholders responsibility to calculate the minimum number of shares that must be purchased
from the stockholder in order for the stockholder to qualify for sale or exchange (rather than distribution) treatment for U.S. federal income tax purposes. Stockholders are urged to consult with their own tax advisers. No assurances can be provided
that a conditional tender will achieve the intended U.S. federal income tax result for any stockholder tendering shares.

Any tendering
stockholder wishing to make a conditional tender must calculate and appropriately indicate the minimum number of shares that must be purchased if any are to be purchased. After the Expiration Time, if the number of shares validly tendered and not
validly withdrawn pursuant to Auction Tenders at a price equal to or less than the Purchase Price and pursuant to Purchase Price Tenders would result in an aggregate purchase price of more than $125 million, so that we must prorate our acceptance of
and payment for tendered shares, we will calculate a preliminary proration percentage, after taking into account the priority given to tenders of odd lots, based upon all shares validly tendered, conditionally or unconditionally, and not validly
withdrawn. If the effect of this preliminary proration would be to reduce the number of shares to be purchased from any tendering stockholder below the minimum number specified by that stockholder, the shares conditionally tendered will
automatically be regarded as withdrawn (except as provided in the next paragraph). All shares tendered by a stockholder subject to a conditional tender and that are withdrawn as a result of proration will be returned at our expense to the tendering
stockholder promptly after the Expiration Time.

After giving effect to these withdrawals, upon the terms and subject to the conditions of
the Offer, we will accept the remaining shares validly tendered, conditionally or unconditionally, on a pro rata basis. If the

withdrawal of conditional tenders would cause the total number of shares to be purchased to fall below an aggregate purchase price of $125 million, then, to the extent feasible, we will select
enough of the shares conditionally tendered that would otherwise have been withdrawn to permit us to purchase such number of shares. In selecting among the conditional tenders, we will select by random lot, treating all tenders by a particular
stockholder as a single lot, and will limit our purchase in each case to the designated minimum number of shares to be purchased. To be eligible for purchase by random lot, stockholders whose shares are conditionally tendered must have validly
tendered all of their shares.

7.

Conditions of the Offer

Notwithstanding any other provision of the Offer, we will not
be required to accept for payment, purchase or pay for any shares tendered, and may terminate or amend the Offer or may postpone the acceptance for payment of, or the purchase of or the payment for shares tendered, subject to the rules under the
Exchange Act, if at any time prior to the Expiration Time, any of the following events or circumstances shall have occurred (or shall have been reasonably determined by us to have occurred):



there shall have been instituted, or there shall be pending, or we shall have received notice of any action, suit, proceeding or application by any government or governmental, regulatory or administrative agency,
authority or tribunal or by any other person, domestic, foreign or supranational, before any court, authority, agency, other tribunal or arbitrator or arbitration panel that directly or indirectly:



challenges or seeks to challenge, restrain, prohibit, delay or otherwise affect the making of the Offer, the acquisition by us of some or all of the shares pursuant to the Offer or otherwise relates in any manner to the
Offer or seeks to obtain material damages in respect of the Offer; or



seeks to make the purchase of, or payment for, some or all of the shares pursuant to the Offer illegal or may result in a delay in our ability to accept for payment or pay for some or all of the shares;



our acceptance for payment, purchase or payment for any shares tendered in the Offer shall violate or conflict with, or otherwise be contrary to, any applicable law, statute, rule, regulation, decree or order;



any action shall have been taken or any statute, rule, regulation, judgment, decree, injunction or order (preliminary, permanent or otherwise) shall have been proposed, sought, enacted, entered, promulgated, enforced or
deemed to be applicable to the Offer or us or any of our subsidiaries by any court, government or governmental agency or other regulatory or administrative authority or body, domestic or foreign, which:



indicates that any approval or other action of any such court, agency or authority may be required in connection with the Offer or the purchase of shares thereunder; or



is reasonably likely to make the purchase of, or payment for, some or all of the shares pursuant to the Offer illegal or to prohibit, restrict or delay consummation of the Offer;



there shall have occurred any of the following:



any general suspension of trading in securities on any United States national securities exchange or in the over-the-counter market, the declaration of a banking moratorium or any suspension of payments in respect of
banks in the United States, whether or not mandatory, or any limitation, whether or not mandatory, by any governmental, regulatory or administrative agency or authority on, or any event that is likely, in our reasonable judgment, to materially
adversely affect, the extension of credit by banks or other lending institutions in the United States;



the commencement or escalation, on or after December 7, 2015, of war, armed hostilities or other international or national calamity, including, but not limited to, an act of terrorism, directly or indirectly
involving the United States;

any decrease of more than 10% in the market price for our common stock or in the Dow Jones Industrial Average, New York Stock Exchange Index, the New York Stock Exchange Composite Index or the Standard and Poors
500 Composite Index measured from the close of trading on December 7, 2015;



any change, condition, event or development, or any condition, event or development involving a prospective change, occurs, is discovered, or is threatened relating to (i) general political, market, economic,
financial or industry conditions in the United States or (ii) our business, general affairs, management, financial position, stockholders equity, income, results of operations, properties, assets, liabilities, condition (financial or
otherwise), income, operations, licenses, franchises, permits, or prospects or in ownership of our shares, which in our reasonable judgment is or may be materially adverse to us or otherwise makes it inadvisable for us to proceed with the Offer; or



in the case of any of the matters described in the preceding four bullets existing at the time of the announcement of the Offer, as applicable, a material acceleration or worsening thereof;



a tender or exchange offer for any or all of our outstanding common stock (other than the Offer), or any merger, amalgamation, acquisition, business combination or other similar transaction with or involving us or any
of our subsidiaries, shall have been proposed, announced or made by any person or entity or shall have been publicly disclosed or we shall have entered into a definitive agreement or an agreement in principle with any person with respect to a
merger, amalgamation, acquisition, business combination or other similar transaction;



we shall have learned that any entity, group (as that term is used in Section 13(d)(3) of the Exchange Act) or person (1) has acquired or proposes to acquire beneficial ownership of more than 5% of
our outstanding common stock, whether through the acquisition of stock, the formation of a group, the grant of any option or right (options for and other rights to acquire shares of our common stock that are acquired or proposed to be acquired being
deemed to be immediately exercisable or convertible for purposes of this clause), or otherwise (other than anyone who publicly disclosed such ownership in a filing with the SEC on or before December 7, 2015), (2) who has filed a Schedule
13D or Schedule 13G with the SEC on or before December 7, 2015 has acquired or proposes to acquire, whether through the acquisition of shares, the formation of a group, the grant of any option or right (options for and other rights to acquire
shares of our common stock that are acquired or proposed to be acquired being deemed to be immediately exercisable or convertible for purposes of this clause), or otherwise (other than by virtue of consummation of the Offer), beneficial ownership of
an additional 1% or more of our outstanding common stock or (3) shall have filed a Notification and Report Form under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, reflecting an intent to acquire us or any of our
subsidiaries or any of our or their respective assets or securities;



any approval, permit, authorization, favorable review or consent or waiver of or filing with any domestic or foreign governmental entity or other authority or any third party consent or notice, required to be obtained
or made in connection with the Offer shall not have been obtained or made on terms and conditions satisfactory to us in our reasonable judgment; or



we shall have determined that the consummation of the Offer and the purchase of the shares pursuant to the Offer is likely, in our reasonable judgment, to cause our common stock to be delisted from the NYSE or eligible
for deregistration under the Exchange Act.

Each of the conditions referred to above is for our sole benefit and may be
asserted or waived by us, in whole or in part, at any time in our discretion prior to the Expiration Time. Any determination by us concerning the fulfillment or non-fulfillment of the conditions described above will be final and binding on all
parties, except as finally determined in a subsequent judicial proceeding if Insperitys determinations are challenged by stockholders.

Our common stock is traded on the NYSE under the
symbol NSP. The following table sets forth the high and low sales prices for the common stock as reported on the NYSE transactional tape.

High

Low

Dividendsper Share

Year Ended December 31, 2015

Fourth quarter (through December 7, 2015)

$

47.52

$

41.88

$0.22

(1)

Third quarter

52.95

41.77

0.22

Second quarter

55.11

47.83

0.22

First quarter

55.42

32.43

0.19

Year Ended December 31, 2014

Fourth quarter

$

34.97

$

27.01

$2.19

Third quarter

33.47

27.29

0.19

Second quarter

33.74

29.82

0.19

First quarter

36.23

26.85

0.17

Year Ended December 31, 2013

Fourth quarter

$

39.69

$

32.67

$0.17

Third quarter

37.80

30.36

0.17

Second quarter

31.80

26.44

0.17

First quarter

34.20

27.04

0.17

1

Payable on December 18, 2015 to stockholders of record at the close of business on December 4, 2015.

On December 7, 2015, the reported closing price of our common stock on the NYSE was $44.03 per share. You are urged to obtain
current market quotations for our common stock before deciding whether, and at what price or prices, to tender your shares pursuant to the Offer.

During 2014 and 2013, we paid aggregate dividends of $69.5 million and $17.4 million, respectively. The payment of dividends is made at the
discretion of our Board of Directors and depends upon our operating results, financial condition, capital requirements, general business conditions and such other factors as our Board of Directors deems relevant.

9.

Source and Amount of Funds

We intend to fund any purchase of shares pursuant to the
Offer, including the related fees and expenses, with borrowings under our revolving credit facility and from cash on hand. The Offer is not subject to a financing contingency. Assuming the Offer is fully subscribed, we expect the aggregate purchase
price for the shares, together with all related fees and expenses, to be approximately $126 million.

We have a $125 million revolving
credit facility (the Facility) with Amegy Bank National Association, as agent, and a syndicate of financial institutions, which may be increased to $150 million based on the terms and subject to the conditions set forth in the
agreement relating to the Facility (the Credit Agreement). The expiration date of the Facility is February 2020. The Facility is available for working capital and general corporate purposes, including acquisitions, and issuances
of letters of credit. Our obligations under the Facility are secured by 65% of the stock of our captive insurance subsidiary and are guaranteed by all of our domestic subsidiaries. Borrowings under the Facility bear interest at an alternate base
rate or LIBOR, at our option, plus an applicable margin. Depending on our leverage ratio, the applicable margin varies (i) in the case of LIBOR loans, from 2.00% to 2.75% and (ii) in the case of alternate base rate loans, from 0.00% to
0.75%. The alternate base rate is the highest of (i) the prime rate most recently published in The Wall Street Journal, (ii) the federal funds rate plus 0.50% and (iii) the 30-day LIBOR rate plus 2.00%. We also pay an unused
commitment fee on the average daily unused portion of the Facility at a rate of 0.25%.

The Facility contains both affirmative and negative covenants. Covenants include, but are not
limited to, limitations on our ability to incur additional indebtedness, sell material assets, retire, redeem or otherwise reacquire our capital stock, acquire the capital stock or assets of another business, make investments and pay dividends. In
addition, the Facility requires us to comply with financial covenants limiting our total funded debt, minimum interest coverage ratio and maximum leverage ratio. At September 30, 2015, we were in compliance with all financial covenants under
the Credit Agreement and had no outstanding borrowings under the Facility. As of September 30, 2015, we had an outstanding $0.6 million letter of credit issued under the Facility.

10.

Certain Information Concerning the Company

The Company. We provide an array of
human resources and business solutions designed to help improve business performance. Since our formation 29 years ago, we have evolved from being solely a professional employer organization (PEO), an industry we pioneered, to our
current position as a comprehensive business performance solutions provider. We were organized as a corporation in 1986 and have provided PEO services since inception.

Our principal executive offices are located at 19001 Crescent Springs Drive, Kingwood, Texas 77339. Our telephone number at that address is
(281) 358-8986 and our website address is www.insperity.com. The information contained on our website, unless otherwise expressly provided herein, is neither part of, nor incorporated by reference into, this Offer to Purchase.

Available Information. We are subject to the informational filing requirements of the Exchange Act, and, accordingly, are obligated to
file reports, statements and other information with the SEC relating to our business, financial condition and other matters. Information, as of particular dates, concerning our directors and executive officers, their remuneration, stock options
granted to them, the principal holders of our securities and any material interest of these persons in transactions with us is required to be disclosed in proxy statements distributed to our stockholders and filed with the SEC. We also have filed a
Tender Offer Statement on Schedule TO (the Schedule TO) with the SEC that includes additional information relating to the Offer.

These reports, statements and other information can be inspected and copied at the public reference facilities maintained by the SEC at 100 F
Street, N.E., Washington, D.C. 20549. Copies of this material may also be obtained by mail, upon payment of the SECs customary charges, from the Public Reference Section of the SEC at 100 F Street, N.E., Room 1580, Washington, D.C. 20549. The
SEC also maintains a website on the Internet at www.sec.gov that contains reports, proxy and information statements and other information regarding registrants that file electronically with the SEC. You may access the Companys publicly
filed documents at this site, including the Schedule TO and the documents incorporated therein by reference. You may obtain information about the Public Reference Room by calling the SEC for more information at 1-800-SEC-0330. You may also go to the
Companys website located at www.insperity.com to access the Schedule TO and related documents.

Incorporation by
Reference. The rules of the SEC allow us to incorporate by reference information into this Offer to Purchase, which means that we can disclose important information to you by referring you to another document filed separately with
the SEC. The following documents that have been previously filed with the SEC contain important information about us and we incorporate them by reference (other than any portions of the respective filings that were furnished to, rather than filed
with, the SEC under applicable SEC rules):



our Annual Report on Form 10-K for the fiscal year ended December 31, 2014;



our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2015, June 30, 2015 and September 30, 2015; and



our Current Reports on Form 8-K as filed with the SEC on February 6, 2015, February 25, 2015, February 27, 2015, March 13, 2015, March 19, 2015, March 23,
2015, April 2, 2015, April 24, 2015, June 11, 2015, and September 1, 2015.

Any statement contained in any document incorporated by reference into this Offer to Purchase
shall be deemed to be modified or superseded to the extent that an inconsistent statement is made in this Offer to Purchase or any subsequently filed document. Any statement so modified or superseded shall not be deemed, except as so modified or
superseded, to constitute a part of this Offer to Purchase.

You can obtain any of the documents incorporated by reference in this Offer
to Purchase from the SECs website at the address or website set forth above.

You may also request a copy of these filings, at no
cost, by writing or telephoning us at the following address:

Insperity, Inc.

19001 Crescent Springs Drive

Kingwood, Texas 77339

Attn:
Corporate Secretary

Telephone: (281) 358-8986

Copies of these filings are also available, without charge, on our website at www.insperity.com. The information contained on our
website is neither part of, nor incorporated by reference into, this Offer to Purchase.

11.

Interests of Directors and Executive Officers; Transactions and Arrangements Concerning the Shares

Shares Outstanding. As of December 1, 2015 we had 24,277,515 shares of our common stock issued and outstanding. Because the
Purchase Price will only be determined after the Expiration Time, the number of shares that will be purchased will not be known until after that time. Assuming that the Offer is fully subscribed, if the Purchase Price is determined to be $43.50 per
share, the minimum Purchase Price under the Offer, the approximate number of shares that would be purchased under the Offer is 2,873,563. Assuming that the Offer is fully subscribed, if the Purchase Price is determined to be $50.00 per share, the
maximum purchase price under the Offer, the approximate number of shares that would be purchased under the Offer is 2,500,000. Assuming that the Offer is fully subscribed, the maximum of 2,873,563 shares that the Company is offering to purchase
under the Offer would represent approximately 11.8% of the total number of shares issued and outstanding as of December 1, 2015. Assuming the Offer is fully subscribed, the minimum of 2,500,000 shares that the Company is offering to purchase
under the Offer would represent approximately 10.3% of the total number of shares issued and outstanding as of December 1, 2015.

Interests of Directors and Executive Officers. As of December 1, 2015, our directors and executive officers as a group (13
persons) beneficially owned an aggregate of 6,020,261 shares, representing approximately 24.77% of the total number of outstanding shares on a fully diluted basis. Our directors and executive officers have advised us that they do not intend to
tender shares in the Offer. We are not aware of any of our affiliates that intend to tender any shares in the Offer. In addition, Starboard, which owned approximately 13.74% of our shares as of December 1, 2015, has advised us that it does not
intend to participate in the Offer. The equity ownership of our directors and executive officers and of Starboard will proportionately increase as a percentage of our outstanding common stock following the consummation of the Offer. Our directors
and executive officers may, subject to applicable law and applicable policies and practices of the Company, sell their shares from time to time in open market transactions at prices that may be more or less favorable than the Purchase Price to be
paid to our stockholders pursuant to the Offer.

The following table sets forth certain information regarding the beneficial ownership of our
common stock as of December 1, 2015 (except as otherwise noted below), by: (i) each person known by the Company to beneficially own 5% or more of our common stock; (ii) each director of the Company; (iii) each of the named
executive officers of the Company; and (iv) all directors and executive officers of the Company as a group.

Name of Beneficial Owner

AmountandNature ofBeneficialOwnership(1)

Percentof Class

Michael W. Brown

36,846

*

Peter A. Feld

3,338,175

(2)

13.75

%

Eli Jones

7,026

*

Carol R. Kaufman

10,181

*

Michelle McKenna-Doyle

1,447

*

Richard G. Rawson

679,741

(3)

2.80

%

Paul J. Sarvadi

1,665,211

(4)

6.86

%

Norman R. Sorensen

2,252

*

Austin P. Young

41,042

*

A. Steve Arizpe

108,173

(5)

*

Jay E. Mincks

54,926

*

Douglas S. Sharp

31,624

*

Daniel D. Herink

43,617

*

Starboard Value LP

3,335,976

(6)

13.74

%

BlackRock Fund Advisors

1,934,767

(7)

7.97

%

The Vanguard Group, Inc.

1,511,629

(8)

6.23

%

Executive Officers and Directors as a group (13 persons)

6,020,261

24.77

%

*

Represents less than 1%.

1

Except as otherwise indicated, each of the stockholders has sole voting and investment power with respect to the securities shown to be owned by such stockholder. The address for each officer and director is in care of
Insperity, Inc., 19001 Crescent Springs Drive, Kingwood, Texas 77339-3802.

2

Includes 2,199 shares held directly and 3,335,976 shares held by Starboard Value LP, based on a Form 4 filed with the SEC on October 1, 2015. Mr. Feld reported shared voting and dispositive power with respect
to 3,335,976 shares. See footnote 6 below for further information.

3

Includes 283,676 shares owned by the RDKB Rawson LP, 249,512 shares owned by the R&D Rawson LP, and 350 shares owned by Dawn M. Rawson (spouse). Mr. Rawson shares voting and investment power over all such
shares with his wife, except for 350 shares owned by his wife.

4

Includes 937,396 shares owned by Our Ship Limited Partnership, Ltd., 463,069 shares owned by the Sarvadi Childrens Limited Partnership, 16,651 shares owned by Paul J. Sarvadi and Vicki D. Sarvadi (spouse), JT WROS
and 19,644 shares owned by six education trusts established for the benefit of the children of Paul J. Sarvadi. Mr. Sarvadi shares voting and investment power over all such shares with his spouse. Also includes 220,000 shares pledged to banks
as collateral for loans.

5

Includes 3,139 shares owned by A. Steve Arizpe and Charissa Arizpe (spouse). Mr. Arizpe shares voting and investment power over all such shares with his wife.

respect to 3,335,976 shares; and (f) Kenneth H. Traub reported sole voting and dispositive power with respect to 4,000 shares. The address of the reporting persons is 777 Third Avenue, 18th
Floor, New York, New York 10017.

7

Based on a Schedule 13G/A filed with the SEC on January 26, 2015. BlackRock, Inc. reported sole voting power with respect to 1,879,422 shares and sole dispositive power with respect to 1,934,767 shares. The address
of BlackRock, Inc. is 40 East 52nd Street, New York, New York 10022.

8

Based on a Schedule 13G/A filed with the SEC on February 10, 2015. The Vanguard Group reported sole voting power with respect to 33,980 shares; sole dispositive power with respect to 1,480,449 shares and shared
dispositive power with respect to 31,180 shares with Vanguard Fiduciary Trust Company. The address of the Vanguard Group is 100 Vanguard Blvd., Malvern, Pennsylvania 19355.

Recent Securities Transactions. Based on our records and information provided to us by our affiliates, directors and executive
officers, neither we nor, to the best of our knowledge, any of our affiliates, directors or executive officers, have effected any transactions in our common stock during the 60 days before the date of this Offer, except as otherwise set forth in
this Offer to Purchase and except for the following open market transactions:

Transaction Party

Date

Numberof Shares

Price

Jay E. Mincks

November 3, 2015

735

$

43.229

*

Jay E. Mincks

November 3, 2015

300

$

44.28

*

Insperity, Inc.

November 330, 2015

178,741

$

43.75

*

*

Reflects the weighted average price.

Additionally, on September 30, 2015, Peter A. Feld,
Carol R. Kaufman and Norman A. Sorensen were issued 404, 517 and 432 shares of common stock, respectively, in lieu of cash compensation for services rendered as board members or on committees thereof.

Equity-Based Compensation. The Company currently maintains the Insperity, Inc. 2012 Incentive Plan (the 2012 Plan) and the
Insperity, Inc. 2001 Incentive Plan ( the 2001 Plan and, together, the Incentive Plans). Under the 2012 Plan, the Company may grant options, restricted stock and other equity awards to eligible persons.

The Compensation Committee of the Board of Directors of the Company is responsible for administering equity-based or other long-term incentive
awards to employees under each of the Incentive Plans. The Compensation Committee may delegate authority to subcommittees when appropriate.

Employee Stock Purchase Plan. The Company maintains an Employee Stock Purchase Plan (ESPP). All employees, including
executive officers, are eligible to participate in the ESPP. Under the ESPP, employees may purchase shares of Company stock through payroll deductions at a discount currently set at 5% of market value. The offering periods under the ESPP are limited
to three or six months in duration. Employees are limited to a maximum payroll deduction of up to a specified percentage of eligible compensation and may not purchase more than $25,000 in shares each calendar year under the ESPP.

Stock Repurchase Program. Our Board of Directors has authorized a program to repurchase shares of our outstanding common stock
(Repurchase Program). The purchases are to be made from time to time in the open market or directly from stockholders at prevailing market prices based on market conditions and other factors. As of December 1, 2015, we were
authorized to repurchase an additional 524,332 shares under the program.

10b5-1 Plans. Several of our executive officers from time
to time execute sales of our common stock under customary 10b5-1 plans between each such executive officer and a broker the (10b5-1 Plans).

Rights Agreement. We and Mellon Investor Services LLC have entered into an amended and
restated Rights Agreement, dated as of November 13, 2007 (the Rights Agreement). Pursuant to the Rights Agreement, each share of our common stock contains a share purchase right (a Right). Each Right
entitles the registered holder to purchase from us a unit consisting of one one-hundredth of a share of Series A Junior Participating Preferred Stock, par value $.10 per share, at a purchase price of $170 per fractional share, subject to adjustment.
The Rights are not exercisable until the earlier of (i) ten days following a public announcement that a person or group of affiliated or associated persons (an Acquiring Person) has acquired, or obtained the right to acquire,
beneficial ownership of 15% or more of our outstanding common stock or (ii) ten business days following the commencement of a tender offer or exchange offer that would result in a persons becoming an Acquiring Person. The Rights expire at
the close of business on November 13, 2017, unless earlier redeemed or exchanged by us. The Rights Agreement and the terms of the Rights, could add substantially to the cost of acquiring the Company, and consequently could delay or prevent a
change in control of the Company.

The foregoing description of the Rights Agreement is qualified in its entirety by reference to the full
text of the Rights Agreement incorporated by reference as Exhibit (a)(d)(14) to the Tender Offer Statement on Schedule TO filed by us on December 8, 2015.

General. Except for (i) the Rights Agreement, (ii) stock options, restricted stock and other awards under the Companys
equity compensation plans, (iii) the Repurchase Program, (iv) the 10b5-1 Plans and (v) as otherwise described in this Offer to Purchase or the documents incorporated by reference herein, none of the Company nor, to the best of the
Companys knowledge, any of its affiliates, directors or executive officers, is a party to any contract, arrangement, understanding or relationship with any other person relating, directly or indirectly, to the Offer or with respect to any
securities of the Company, including, but not limited to, any contract, arrangement, understanding or relationship concerning the transfer or the voting of securities, joint ventures, loan or option arrangements, puts or calls, guaranties of loans,
guaranties against loss or the giving or withholding of proxies, consents or authorizations.

Please see our periodic and current reports
and proxy statements filed with the SEC for detailed descriptions of the arrangements disclosed above. In addition, copies of the agreements or forms of the agreements disclosed above have been filed with the SEC.

12.

Effects of the Offer on the Market for Shares; Registration under the Exchange Act

The
purchase by us of shares of our common stock pursuant to the Offer will reduce the number of shares of our common stock that might otherwise be traded publicly and is likely to reduce the number of stockholders.

We believe that there will be a sufficient number of shares of our common stock outstanding and publicly traded following completion of the
Offer to ensure a continued trading market for the shares. Based upon published guidelines of the NYSE, we do not believe that our purchase of shares under the Offer will cause the remaining outstanding shares to be delisted from the NYSE. The Offer
is conditioned upon, among other things, our determination that the consummation of the Offer and the purchase of shares will not cause the shares to be delisted from the NYSE. See Section 7.

The shares are currently margin securities under the rules of the Federal Reserve Board. This has the effect, among other things,
of allowing brokers to extend credit to their customers using such shares as collateral. We believe that, following the purchase of shares under the Offer, the shares will continue to be margin securities for purposes of the Federal
Reserve Boards margin rules and regulations.

Our common stock is registered under the Exchange Act, which requires, among other
things, that we furnish certain information to our stockholders and the SEC and comply with the SECs proxy rules in connection with meetings of our stockholders. We believe that our purchase of shares under the Offer pursuant to the terms of
the Offer will not result in our common stock becoming eligible for deregistration under the Exchange Act.

It is a condition of our obligation to purchase shares pursuant to the Offer that as a result of
the consummation of the Offer, there not be a reasonable likelihood that our common stock will be eligible for deregistration under the Exchange Act.

13.

Legal Matters; Regulatory Approvals

Except as described in this Offer to Purchase, we
are not aware of any license or regulatory permit that appears to be material to our business that might be adversely affected by our acquisition of shares as contemplated by the Offer or of any approval or other action by any government or
governmental, administrative or regulatory authority or agency, domestic or foreign, that would be required for our acquisition or ownership of shares as contemplated by the Offer.

Our obligation to accept for payment and pay for shares under the Offer is subject to various conditions. See Section 7.

14.

Material U.S. Federal Income Tax Consequences

The following discussion is a summary of
material U.S. federal income tax consequences to our stockholders of an exchange of shares for cash pursuant to the Offer. This discussion is general in nature and does not discuss all aspects of U.S. federal income taxation that may be relevant to
a particular stockholder in light of the stockholders particular circumstances, or to certain types of stockholders subject to special treatment under U.S. federal income tax laws (such as insurance companies, tax-exempt organizations,
regulated investment companies, real estate investment trusts, U.S. Holders (as defined below) whose functional currency is not the U.S. dollar, partnerships or other entities or arrangements treated as partnerships or pass-through
entities for U.S. federal income tax purposes (or their investors or beneficiaries), persons holding shares as part of a hedging, integrated, conversion or constructive sale transaction or a straddle, financial institutions, brokers, dealers in
securities or currencies, traders that elect to mark-to-market their securities, certain expatriates or former long-term residents of the United States or personal holding companies). In addition, this discussion does not consider the effect of any
alternative minimum taxes or foreign, state, local or other tax laws, or any U.S. tax considerations (e.g., estate or gift tax) other than U.S. federal income tax considerations, that may be applicable to particular stockholders. Further,
this discussion assumes that stockholders hold their shares as capital assets (generally, property held for investment) within the meaning of Section 1221 of the Internal Revenue Code of 1986, as amended (the
Code) and generally assumes that they did not receive their shares through the exercise of employee stock options or otherwise as compensation. In addition, the discussion assumes that the provisions of Section 5881 of the
Code are not applicable to any payments made pursuant to the Offer.

If a partnership or other entity or arrangement treated as a
partnership for U.S. federal income tax purposes holds shares, the tax treatment of a partner generally will depend upon the status of the partner and the activities of the partnership. A partnership holding shares and partners in such partnership
should consult their own tax advisers about the U.S. federal income tax consequences of an exchange of shares for cash pursuant to the Offer.

This discussion is based on the Code and applicable U.S. Treasury regulations, rulings, administrative pronouncements and judicial decisions
thereunder as of the date hereof, all of which are subject to change or differing interpretations at any time with possible retroactive effect.

We have not sought, nor will we seek, any ruling from the IRS with respect to the matters discussed below. There can be no assurances that the
IRS will not take a different position concerning tax consequences of the sale of shares to us pursuant to the Offer or that any such position would not be sustained.

As used herein, a U.S. Holder means a beneficial owner of shares that is for U.S. federal income tax purposes (1) an
individual citizen or resident alien of the United States, (2) a corporation (or other entity taxed as a corporation) created or organized in or under the laws of the United States or any state thereof or the District of

Columbia, (3) an estate the income of which is subject to U.S. federal income taxation regardless of its source or (4) a trust if (x) the administration of the trust is subject to
the primary supervision of a court within the United States and one or more United States persons have the authority to control all substantial decisions of the trust, or (y) it has a valid election in effect under applicable U.S. Treasury
regulations to be treated as a United States person. As used herein, a Non-U.S. Holder means a beneficial owner of shares that is neither (i) a U.S. Holder, nor (ii) a partnership or other entity or arrangement
classified as a partnership for U.S. federal income tax purposes.

Each stockholder is advised to consult its own tax adviser to
determine the U.S. federal, state, local, foreign and other tax consequences to it of the Offer.

Consequences to Stockholders Who
Do Not Participate in the Offer. Stockholders who do not participate in the Offer will not incur any U.S. federal income tax as a result of the exchange of shares for cash by other stockholders pursuant to the Offer.

Consequences to U.S. Holders. An exchange of shares for cash pursuant to the Offer generally will be treated as either a taxable sale
or exchange or as a taxable distribution with respect to such shares.

If the receipt of cash by a U.S. Holder in exchange for the tender
of shares pursuant to the Offer is treated as a sale or exchange (as described below) of such shares for U.S. federal income tax purposes pursuant to Section 302 of the Code, the U.S. Holder will recognize capital gain or loss equal to the
difference between (1) the amount of cash received by the U.S. Holder for such shares and (2) the U.S. Holders adjusted tax basis for such shares at the time of the sale. Generally, a U.S. Holders adjusted tax basis
for the shares will be equal to the cost of the shares to the U.S. Holder, decreased (but not below zero) by the amount of any previous distributions treated as a tax-free return of capital. This gain or loss will be characterized as long-term
capital gain or loss if the U.S. Holders holding period for the shares that were sold exceeds one year as of the date we are treated as purchasing the shares in the Offer for U.S. federal income tax purposes. A U.S. Holder that is an
individual, trust or estate is generally eligible for a reduced rate of U.S. federal income tax on long-term capital gain. A U.S. Holders ability to deduct capital losses may be limited. A U.S. Holder must calculate gain or loss separately for
each block of shares (generally, shares acquired at the same cost in a single transaction) that we purchase from the U.S. Holder under the Offer.

A U.S. Holders exchange of shares for cash pursuant to the Offer will be treated as a sale or exchange of the shares for U.S. federal
income tax purposes pursuant to Section 302 of the Code if the exchange:



results in a complete termination of the stockholders stock interest in us under Section 302(b)(3) of the Code;



is a substantially disproportionate redemption with respect to the stockholder under Section 302(b)(2) of the Code; or



is not essentially equivalent to a dividend with respect to the stockholder under Section 302(b)(1) of the Code.

In determining whether any of these tests have been met, a U.S. Holder must take into account not only the stock that the stockholder actually
owns, but also the stock that it constructively owns within the meaning of Section 318 of the Code (as modified by Section 302(c) of the Code). Under these constructive ownership rules, a stockholder will be considered to own those shares
of stock owned, directly or indirectly, by certain members of the stockholders family and certain entities (such as corporations, partnerships, trusts and estates) in which the stockholder has an equity interest, as well as shares of stock the
stockholder has an option to purchase. U.S. Holders should consult their own tax advisers with respect to the operation of these constructive ownership rules.

One of the following tests must be satisfied with respect to the U.S. Holder in order for the exchange of shares for cash to be treated as a
sale or exchange by that stockholder for U.S. federal income tax purposes. Due

to the factual nature of these tests, stockholders should consult their tax advisers to determine whether the purchase of their shares in the Offer qualifies for sale or exchange treatment in
their particular circumstances.

A distribution to a stockholder will result in a complete termination of the
stockholders equity interest in us if either (1) all of the shares of stock in us actually and constructively owned by the stockholder are exchanged for cash pursuant to the Offer or (2) all of the shares of stock in us actually
owned by the stockholder are exchanged for cash pursuant to the Offer and the stockholder is eligible to waive, and effectively waives, the attribution of all shares of stock in us constructively owned by the stockholder in accordance with the
procedures described in Section 302(c)(2) of the Code. A U.S. Holder may also satisfy the complete termination test if, in the same transaction, some of its shares of stock in us are redeemed and all of the remainder of its shares
of stock in us are sold or otherwise transferred to a third party so that after the transaction the U.S. Holder no longer owns (actually or constructively) any shares of stock in us. U.S. Holders wishing to satisfy the complete
termination test through waiver of attribution in accordance with the procedures described in Section 302(c)(2) of the Code should consult their own tax advisers concerning the mechanics and desirability of such a waiver.

A distribution to a stockholder generally will result in a substantially disproportionate redemption if the percentage of the
outstanding shares of stock in us actually and constructively owned by the stockholder immediately following the exchange of shares for cash pursuant to the Offer is less than 80% of the percentage of the outstanding shares of stock in us actually
and constructively owned by the stockholder immediately before the exchange (treating as outstanding all shares purchased in the Offer from the particular stockholder and all other stockholders).

A distribution to a stockholder is not essentially equivalent to a dividend if it results in a meaningful reduction in
the stockholders stock interest in us. Whether a stockholder meets this test will depend on the stockholders particular facts and circumstances. The IRS has indicated in a published revenue ruling that even a small reduction in the
percentage interest of a stockholder whose relative stock interest in a publicly held corporation is minimal and who exercises no control over corporate affairs should constitute a meaningful reduction. Stockholders should consult their
tax advisers as to the application of this test to their particular circumstances.

Each stockholder should be aware that because
proration may occur in the Offer, even if all the shares of stock in us actually and constructively owned by a stockholder are tendered pursuant to the Offer, fewer than all of the shares tendered may be purchased by us unless the tendering
stockholder has made a conditional tender. See Section 6. Thus, proration may affect whether the surrender by a stockholder pursuant to the Offer will meet any of the three tests under Section 302 of the Code.

If a U.S. Holders receipt of cash attributable to an exchange of shares for cash pursuant to the Offer does not meet one of the tests of
Section 302 of the Code described above, then the full amount of cash received by the U.S. Holder with respect to our purchase of shares under the Offer will be treated as a distribution to the U.S. Holder with respect the U.S. Holders
shares and will be treated as ordinary dividend income to the U.S. Holder to the extent of such stockholders ratable share of our current or accumulated earnings and profits as determined under U.S. federal income tax principles. Provided
certain holding period requirements and other conditions are satisfied, non-corporate U.S. Holders generally will be subject to U.S. federal income tax at a maximum rate of 20% with respect to any such dividend income. To the extent that the amount
of the distribution exceeds our current and accumulated earnings and profits, the excess first will be treated as a return of capital that will reduce the U.S. Holders adjusted tax basis in the shares exchanged in the Offer. Any amount
remaining after the U.S. Holders adjusted tax basis has been reduced to zero will be taxable to the U.S. Holder as capital gain realized on the sale or exchange of such shares. The redeemed stockholders basis in the redeemed shares
(after any reduction as noted above) will be allocated to other shares of stock in us held by the redeemed stockholder. A dividend received by a corporate U.S. Holder may be (1) eligible for a dividends-received deduction (subject to applicable
exceptions and limitations) and (2) subject to the extraordinary dividend provisions of Section 1059 of the Code. Corporate stockholders should consult their own tax advisers regarding the U.S. federal tax consequences of the
Offer in relation to their particular facts and circumstances.

Consequences to Non-U.S. Holders. Gain realized by a Non-U.S. Holder on an exchange of
shares for cash pursuant to the Offer generally will not be subject to U.S. federal income tax if the exchange is treated as a sale or exchange for U.S. federal income tax purposes pursuant to the tests of Section 302 of the Code described
above unless (1) such gain is effectively connected with the conduct by such Non-U.S. Holder of a trade or business in the United States (and, if an applicable income tax treaty applies, the gain is attributable to a United States permanent
establishment or fixed base maintained by such Non-U.S. Holder), (2) in the case of gain realized by a Non-U.S. Holder that is an individual, such Non-U.S. Holder is present in the United States for 183 days or more in the taxable year of the
exchange and certain other conditions are met, or (3) our shares that are exchanged constitute a United States real property interest.

Non-U.S. Holders described in clause (1) above will be subject to U.S. federal income tax on a net income basis at applicable graduated
U.S. federal income tax rates in much the same manner as if such Non-U.S. Holder were a resident of the United States, and in the case of a corporate Non-U.S. Holder, such Non-U.S. Holder may be subject to a branch profits tax at a 30% rate, or a
lower rate specified in an applicable income tax treaty. An individual described in clause (2) above will be taxed on his or her gains at a flat rate of 30% (or such lower rate as may be specified by an applicable income tax treaty), which may
be offset by certain U.S. source capital losses of such Non-U.S. Holder provided that such Non-U.S. Holder has timely filed U.S. federal income tax returns with respect to such losses.

Our shares will constitute a United States real property interest with respect to a Non-U.S. Holder if (1) we are or have been a
United States real property holding corporation for U.S. federal income tax purposes at any time during the shorter of (i) the period during which the Non-U.S. Holder held such shares or (ii) the 5-year period ending on the
date the Non-U.S. Holder exchanges such shares pursuant to the Offer and (2) the Non-U.S. Holder actually or constructively owns or has owned (at any time during the shorter of such periods) more than 5% of our shares. We do not believe that we
have been a United States real property holding corporation at any time during the 5-year period preceding the sale pursuant to the Offer.

If a Non-U.S. Holder does not satisfy any of the Section 302 tests explained above, the full amount received by the Non-U.S. Holder with
respect to our purchase of shares under the Offer will be treated as a distribution to the Non-U.S. Holder with respect to the Non-U.S. Holders shares, rather than as an amount received in a sale or exchange of such shares. Because
satisfaction of the Section 302 tests is dependent on matters of fact, the Depositary, or other withholding agent, will presume, for withholding purposes, that all amounts paid to Non-U.S. Holders in exchange for their shares are distributions.
The treatment, for U.S. federal income tax purposes, of such distribution as a dividend, a tax-free return of capital or a capital gain from the sale of shares, and the reallocation of the basis of the redeemed shares, will be determined in the
manner described above (see  Consequences to U.S. Holders). However, the Depositary, or other withholding agent, generally will treat amounts received by a Non-U.S. Holder with respect to our purchase of shares under the Offer as
dividends and not as tax-free returns of capital or capital gains distributions, and such dividends will be subject to withholding of U.S. federal income tax at the rate of 30% or such lower rate as may be specified by an applicable income tax
treaty, provided we have received proper certification of the application of such income tax treaty, unless such dividends are effectively connected with a Non-U.S. Holders conduct of a trade or business within the United States. Non-U.S.
Holders should consult their own tax advisers regarding their entitlement to benefits under an applicable income tax treaty and the manner of claiming the benefits of such treaty. If any amounts withheld exceed the Non-U.S. Holders U.S.
federal income tax liability, such Non-U.S. Holder may obtain a refund or credit of any excess amounts withheld by filing an appropriate claim for a refund with the IRS. Amounts treated as dividends that are effectively connected with a Non-U.S.
Holders conduct of a trade or business in the United States and, if required by an applicable income tax treaty, are attributable to a permanent establishment or fixed base in the United States, are generally taxed in the manner applicable to
U.S. Holders, as described above. In such cases, the Non-U.S. Holder will not be subject to withholding so long as such Non-U.S. Holder complies with applicable certification and disclosure requirements (such as providing a validly completed IRS
Form W-8ECI). In addition, dividends received by a foreign corporation that are effectively connected with the conduct of

a trade or business in the United States may be subject to a branch profits tax at a 30% rate, or a lower rate specified in an applicable income tax treaty. See Section 3 with respect to the
application of U.S. federal income tax withholding to payments made to Non-U.S. Holders.

Additional Tax on Net Investment Income.
An additional 3.8% tax will be imposed on the net investment income of certain U.S. citizens and resident aliens, and on the undistributed net investment income of certain estates and trusts. Among other items, net
investment income generally includes gross income from dividends and net gain from the disposition of property, such as the shares, less certain deductions. Stockholders should consult their own tax advisers with respect to this additional
tax.

United States Federal Income Tax Backup Withholding. See Section 3 with respect to the U.S. federal income tax backup
withholding requirements.

FATCA. Sections 1471 through 1474 of the Code (commonly referred to as FATCA)
generally impose a U.S. federal withholding tax of 30% on dividend income from our shares if paid to a foreign financial institution or a non-financial foreign entity (each as defined in the Code) (including, in some cases,
when such foreign financial institution or non-financial foreign entity is acting as an intermediary for the beneficial owner), unless those entities comply with a complicated U.S. information reporting, disclosure and certification regime. As
described above, the Depositary, or other withholding agent, generally will treat amounts paid pursuant to the Offer as a dividend, and, therefore, such amounts may be subject to FATCA withholding. If the Depositary, or other withholding agent,
withholds tax under FATCA, it will not also withhold the 30% U.S. federal income tax described above. Stockholders should consult their own tax advisers regarding the possible impact FATCA may have on an exchange of shares for cash pursuant to the
Offer.

This discussion is general in nature and does not discuss all aspects of U.S. federal income taxation that may be
relevant to a particular stockholder in light of the stockholders particular circumstances, or to certain types of stockholders subject to special treatment under U.S. federal income tax laws. You are advised to consult with your own tax
adviser to determine the particular tax consequences to you of the Offer, including the applicability and effect of state, local and foreign tax laws.

15.

Extension of the Offer; Termination; Amendment

We expressly reserve the right, in our
sole discretion and subject to applicable law, at any time and from time to time, and regardless of whether or not any of the events set forth in Section 7 shall have occurred or shall be deemed by us to have occurred, to extend the period of
time the Offer is open and delay acceptance for payment of, and payment for, any shares by giving oral or written notice of such extension to the Depositary and making a public announcement of such extension. We also expressly reserve the right, in
our sole discretion, to terminate the Offer and reject for payment and not pay for any shares not theretofore accepted for payment or paid for, subject to applicable law, and to postpone payment for shares, upon the occurrence of any of the
conditions specified in Section 7, by giving oral or written notice of such termination or postponement to the Depositary and making a public announcement of such termination or postponement. Our reservation of the right to delay payment for
shares that we have accepted for payment is limited by Rule 13e-4(f)(5) under the Exchange Act, which requires that we must pay the consideration offered or return the shares tendered promptly after termination or withdrawal of the Offer.

Subject to compliance with applicable law, we further reserve the right, in our sole discretion, to amend the Offer in any respect
(including, without limitation, by decreasing or increasing the consideration per share offered pursuant to the Offer to stockholders or by decreasing or increasing the aggregate purchase price of shares being sought in the Offer). Amendments to the
Offer may be made at any time and from time to time by public announcement of such amendments. In the case of an extension, the notice of the amendment must be issued no later than 9:00 a.m., New York City time, on the next business day after the
last previously scheduled or announced Expiration Time. Any public announcement made pursuant to the Offer will be disseminated

promptly to stockholders in a manner reasonably designed to inform stockholders of such change. Without limiting the manner in which we may choose to make a public announcement, except as
required by applicable law, we shall have no obligation to publish, advertise or otherwise disseminate any such public announcement other than by making a release through BusinessWire or another comparable service.

If we materially change the terms of the Offer or the information concerning the Offer, or if we waive a material condition of the Offer, we
will extend the Offer to the extent required by Rules 13e-4(d)(2), 13e-4(e)(3) and 13e-4(f)(1) promulgated under the Exchange Act. These rules and certain related releases and interpretations of the SEC provide that the minimum period during which a
tender offer must remain open following material changes in the terms of the tender offer or information concerning the tender offer (other than a change in price or a change in percentage of securities sought) will depend on the facts and
circumstances, including the relative materiality of such terms or information. If:



we increase or decrease the price to be paid for shares or increase by more than 2% of the outstanding shares or decrease the number of shares sought in the Offer; and



the Offer is scheduled to expire at any time earlier than the expiration of a period ending on the tenth business day from, and including, the date that notice of such an increase or decrease is first published, sent or
given to stockholders in the manner specified in this Section 15,

then, in each case, the Offer will be extended so that it
will remain open for a period of ten business days from and including the date that such increase or decrease is first published, sent or given to stockholders in the manner specified in this Section 15. For purposes of the Offer, a
business day means any day other than a Saturday, Sunday or Federal holiday and consists of the time period from 12:01 a.m. through 12:00 Midnight, New York City time.

16.

Fees and Expenses

We have retained Credit Suisse Securities (USA) LLC to act as our
Dealer Manager in connection with the Offer.

The Dealer Manager will receive customary compensation in connection with the Offer. We have
also agreed to reimburse the Dealer Manager for reasonable out-of-pocket expenses incurred in connection with the Offer, including reasonable fees and expenses of counsel, and to indemnify the Dealer Manager against various liabilities in connection
with the Offer, including liabilities under the U.S. federal securities laws.

The Dealer Manager and its affiliates have provided, and
may in the future provide, various investment banking and other services to us for which they have received, or we expect they will receive, customary compensation from us.

The Dealer Manager and its affiliates, in the ordinary course of their respective businesses, may purchase and/or sell our securities,
including the shares, for its own account and for the account of its customers. As a result, the Dealer Manager and its affiliates at any time may own certain of our securities, including the shares. In addition, the Dealer Manager and its
affiliates may tender shares into the Offer for its own account.

We have also retained Innisfree M&A Incorporated to act as
Information Agent and Computershare Trust Company, N.A. to act as Depositary in connection with the Offer. The Information Agent may contact stockholders by mail, telephone, facsimile and personal interviews and may request brokers, dealers and
other nominee stockholders to forward materials relating to the Offer to beneficial owners. The Information Agent and the Depositary will each receive reasonable and customary compensation for their respective services, will be reimbursed by us for
reasonable out-of-pocket expenses incurred in connection with the Offer and will be indemnified against certain liabilities in connection with the Offer, including certain liabilities under the federal securities laws.

The Information Agent and its affiliates have provided, and may in the future provide, various
proxy and other services to us for which they have received, or we expect they will receive, customary compensation from us.

We will not
pay any fees or commissions to brokers, dealers or other persons (other than fees to the Dealer Manager, the Information Agent and the Depositary as described above) for soliciting tenders of shares pursuant to the Offer. Stockholders holding shares
through brokers, dealers, commercial banks, trust companies or other nominee stockholders are urged to consult the brokers, dealers or other nominee stockholders to determine whether transaction costs may apply if stockholders tender shares through
the brokers, dealers or other nominee stockholders and not directly to the Depositary. We will, however, upon request, reimburse brokers, dealers, commercial banks and trust companies for customary mailing and handling expenses incurred by them in
forwarding the Offer and related materials to the beneficial owners of shares held by them as a nominee or in a fiduciary capacity. No broker, dealer, commercial bank or trust company has been authorized to act as our agent, the Information Agent,
the Dealer Manager or the Depositary for purposes of the Offer. We will pay or cause to be paid all stock transfer taxes, if any, on our purchase of shares, except as otherwise provided in Section 5 hereof.

Certain officers and employees of the Company may render services in connection with the Offer but will not receive any additional
compensation for such services.

17.

Miscellaneous

We are not aware of any jurisdiction where the making of the Offer is not
in compliance with applicable law. If we become aware of any jurisdiction within the United States where the making of the Offer or the acceptance of shares pursuant to the Offer is not in compliance with any valid applicable law, we will make a
good faith effort to comply with the applicable law. If, after such good faith effort, we cannot comply with the applicable law, the Offer will not be made to (nor will tenders be accepted from or on behalf of) the holders of shares in that
jurisdiction. In any jurisdiction where the securities or blue sky laws require the Offer to be made by a licensed broker or dealer, the Offer shall be deemed to be made on our behalf by the Dealer Manager or one or more registered brokers licensed
under the laws of such jurisdiction.

After completing the Offer, we may purchase additional shares in the open market subject to market
conditions. We may also purchase shares in private transactions, tender offers or otherwise. Any of these purchases may be on the same terms as, or on terms more or less favorable to stockholders than, the terms of the Offer. However, Rule 13e-4
under the Exchange Act generally prohibits us and our affiliates from purchasing any shares, other than through the Offer, until at least 10 business days after the expiration or termination of the Offer. Any possible future purchases by us will
depend on many factors, including the market price of the shares, the results of the Offer, our business and financial position and general economic and market conditions.

Pursuant to Rule 13e-4(c)(2) under the Exchange Act, we have filed with the SEC the Schedule TO, which contains additional information
relating to the Offer. The Schedule TO, including the exhibits and any amendments and supplements thereto, may be examined, and copies may be obtained, at the same places and in the same manner as is set forth in Section 10 with respect to
information concerning Insperity.

We have not authorized any person to make any recommendation on our behalf as to whether you should
tender or refrain from tendering your shares in the Offer or as to the price or prices at which you may choose to tender your shares in the Offer. You should rely only on the information contained in this Offer to Purchase and in the Letter of
Transmittal or to documents to which we have referred you. Our delivery of this Offer to Purchase shall not under any circumstances create any implication that the information contained in this Offer to Purchase is correct as of any time other than
the date of this Offer to Purchase or that there have been no changes in the information included or incorporated by reference

herein or in the affairs of Insperity or any of its subsidiaries or affiliates since the date hereof. We have not authorized anyone to provide you with information or to make any representation
in connection with the Offer other than the information and representations contained in this Offer to Purchase or in the Letter of Transmittal. If anyone makes any recommendation or gives any information or representation, you must not rely upon
that recommendation, information or representation as having been authorized by us, the Dealer Manager, the Depositary or the Information Agent.

The Letter of Transmittal, certificates for shares and any other required documents should be
sent or delivered by each stockholder of the Company or his or her broker, dealer, commercial bank, trust company or other nominee to the Depositary as follows:

The Depositary for the Offer is:

If delivering by First Class Mail:

Computershare Trust
Company, N.A.

c/o Voluntary Corporate Actions

P.O. Box 43011

Providence, RI 02940-3011

If delivering by Certified, Express,

or Overnight Delivery:

Computershare Trust Company, N.A.

c/o Voluntary Corporate Actions

250
Royall Street, Suite V

Canton, MA 02021

DELIVERY OF THE LETTER OF TRANSMITTAL TO AN ADDRESS OTHER THAN AS SET FORTH ABOVE WILL NOT CONSTITUTE A VALID
DELIVERY TO THE DEPOSITARY.

Questions and requests for assistance may be directed to the Information Agent or the Dealer Manager at their
respective telephone numbers and addresses set forth below. Requests for additional copies of this Offer to Purchase, the Letter of Transmittal or the Notice of Guaranteed Delivery should be directed to the Information Agent. The Information Agent
will promptly furnish to stockholders additional copies of these materials at the Companys expense. You may also contact your broker, dealer, commercial bank, trust company or other nominee for assistance concerning the Offer.